Streambed substrate composition and macroinvertebrate communities in the presence of a dam


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Streambed substrate composition and macroinvertebrate communities in the presence of a dam

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Streambed substrate composition and macroinvertebrate communities in the presence of a dam
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Goldstein, Julia
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The construction of dams to satiate human year-round water needs has been so extensive in the past 50 years that small streams are some of the world’s only water flows to still run unregulated (Allan, 1995; Vitousek et al., 1997). That said, plenty of small stream water regimes are regulated, and the effects of this on biodiversity are under-investigated, especially in the tropics (Allan, 1995). In this study the effects of a small dam on the physical environment and macroinvertebrate communities of a tropical montane stream, the Quebrada Máquina, in Monteverde, Costa Rica, were analyzed. Substrate composition, temperature and macroinvertebrate diversity were measured between April 8 and May 4, 2006. I collected1592 macroinvertebrates and identified them to family and morphospecies level, over two-thirds of these individuals coming from the order Diptera. On a biological level, the numbers of orders and morphospecies decreased significantly as distance to the dam decreased. Physically, temperature increased significantly between 50 m upstream of the dam and 50 m downstream. Relative percentage of sand as substrate (RPSS) decreased significantly as distance from the dam decreased, and sediment as a substrate increased significantly at sites closer to the dam. While some of this study’s conclusions are unique to the Quebrada Máquina, many of its findings are universal to stream-dam situations. Taking what can be generalized from this experiment, I propose conservation strategies relevant to all dammed aquatic ecosystems. ( ,, )
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La construcción de represas durante los últimos 50 años ha sido tan extensa que las quebradas pequeñas son de las únicas fuentes de agua que corren sin regulación alguna (Allan, 1995; Vitousek et al., 1997). Sin embargo, muchas quebradas pequeñas son reguladas, y los efectos de esta actividad en la biodiversidad no han recibido mucha atención científica, especialmente en los trópicos (Allan, 1995). En esta investigación se analizaron los efectos de una represa pequeña en el ambiente físico y en las comunidades de macroinvertebrados de una quebrada tropical y montañosa, la quebrada Máquina, en Monteverde, Costa Rica. Se midió la composición del sustrato, la temperatura y la diversidad de macroinvertebrados entre el 8 de abril y el 4 de mayo del 2006. Se colectaron1592 macroinvertebrados y se identificaron a los niveles de familia y especie morfológica; más de las dos terceras partes de la muestra pertenecieron al orden Diptera. Biológicamente, los números de órdenes y especies morfológicas disminuyeron significativamente en sitios cercanos a la represa. Físicamente, la temperatura aumentó significativamente entre los 50 m arriba de la represa y los 50 m debajo de la represa. El porcentaje relativo de arena como sustrato (PRAS) disminuyó significativamente en sitios cercanos a la represa y el sedimento como sustrato subió significativamente en estos mismos sitios. Aunque algunas de las conclusiones solamente pueden ser aplicadas a la quebrada Máquina, muchas otras son comunes a sistemas de quebradas con represas. Se proponen estrategias de conservación aplicables a todos los ecosistemas acuáticos con represas basadas en generalizaciones inferidas de los resultados obtenidos.
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1 Streambed substrate composition and macroinvertebrate communities in the presence of a dam Julia Goldstein Department of Neuroscience, Pomona College ABSTRACT The construction of dams to satiate human year round water needs has been so extensive in t he past 50 years that small streams are some of the world s only water flows to still run unregulated Allan, 1995; Vitousek et al., 1997. That said, plenty of small stream water regimes are regulated, and the effects of this on biodiversity are under in vestigated, especially in the tropics Allan, 1995. In this study the effects of a small dam on the physical environment and macroinvertebrate communities of a tropical montane stream, the Quebrada Máquina, in Monteverde, Costa Rica, were analyzed. Subst rate composition, temperature and macroinvertebrate diversity were measured be tween April 8 and May 4, 2006. I collected1592 macroinvertebrates and identified them to family and morphospecies level, over two thirds of these individuals coming from the ord er Diptera. On a biological level, the numbers of orders and morphospecies decreased significantly as distance to the dam decreased. Physically, temperature increased significantly between 50 m upstream of the dam and 50 m downstream. Relative percentag e of sand as substrate RPSS decreased significantly as distance from the dam decreased, and sediment as a substrate increased significantly at sites closer to the dam. While some of this study s conclusions are unique to the Quebrada Máquina, many of it s findings are universal to stream dam situations. Taking what can be generalized from this experiment, I propose conservation strategies relevant to all dammed aquatic ecosystems . RESUMEN La construcción de represas durante los últimos 50 años ha sido tan extensa que las quebradas pequeñas son de las únicas fuentes de agua que corren sin regulación alguna Allan, 1995; Vitousek et al., 1997. Sin embargo, muchas quebradas pequeñas son reguladas, y los efectos de esta actividad en la biodiversidad no han recibido mucha atención científica, especialmente en los trópicos Allan, 1995. En esta investigación se analizaron los efectos de una represa pequeña en el ambiente físico y en las comunidades de macroinvertebrados de una quebrada tropical y mon tañosa, la quebrada Máquina, en Monteverde, Costa Rica. Se midió la composición del sustrato, la temperatura y la diversidad de macroinvertebrados entre el 8 de abril y el 4 de mayo del 2006. Se colectaron1592 macroinvertebrados y se identificaron a los niveles de familia y especie morfológica; más de las dos terceras partes de la muestra pertenecieron al orden Diptera. Biológicamente, los números de órdenes y especies morfológicas disminuyeron significativamente en sitios cercanos a la represa. Física mente, la temperatura aumentó significativamente entre los 50 m arriba de la represa y los 50 m debajo de la represa. El porcentaje relativo de arena como sustrato PRAS disminuyó significativamente en sitios cercanos a la represa y el sedimento como sus trato subió significativamente en estos mismos sitios. Aunque algunas de las conclusiones solamente pueden ser aplicadas a la quebrada Máquina, muchas otras son comunes a sistemas de quebradas con represas. Se proponen estrategias de conservación aplicab les a todos los ecosistemas acuáticos con represas basadas en generalizaciones inferidas de los resultados obtenidos. INTRODUCTION Stream ecosystems are dynamic and support great biodiversity. They serve as breeding grounds for numerous amphibian While s, 2006 and insect species, facilitate migration of

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2 various freshwater fauna and provide local terrestrial communities with a source of water. Humans are very important consumers of stream water. Historically, humans have altered flow regimes of rivers and streams of all sizes in order to meet their year round water needs. Dam building climaxed world wide between 1950 and 1980 and was so prolific that today in the United States only two percent of rivers flow unimpeded Allan, 1995; Vitousek et al., 199 7. In less developed countries the zenith of dam construction did not come until more recently, and in many tropical countries dam building is still accelerating Allan, 1995. Small streams are particularly sensitive to water regulation and in areas wi th pronounced dry seasons they may even run dry if impeded Sand Jensen, 2001. Unfortunately, small streams are also the least protected, even though anthropogenic interference proves their greatest threat Benke, 1990. Freshwater organisms and ecosyst em inventories have not been a priority for scientists, thus the degradation of these communities by dams and other man made constructions is not well understood. This troubling phenomenon is more pronounced in the tropics Benke, 1990. What is known ab out the effects of dams on stream environment and biodiversity has mostly been inferred from studies of large dams on large rivers. By interrupting the natural flow of streams and rivers, dams of all sizes alter abiotic factors which in turn directly affec t aquatic flora and fauna Wood and Armitage, 1997; Rancourt, 2004. Directly upstream from a dam, water flow is reduced and a reservoir forms. This decrease in flow regime and discharge causes the settling of sediment and subsequently the bottom is dispr oportionately sandy Allan, 1995. The area downstream from a dam receives water stripped of most sediment which then scours the streambed and picks up small particles as it flows downstream at modified speeds Allan, 1995. Both of these effects contrib ute to decreasing habitat heterogeneity for macroinvertebrates. Sandy streambeds have the lowest macroinvertebrate diversity and rocky ones have highest diversity Stevens, 1996. As large rock abundance increases, smaller interstitial rock presence prod uces higher habitat diversity, and more microhabitat variation arises Hyman, 2002. Increased microhabitat variation means increased macroinvertebrate diversity, thus rocky substrates house more biotic diversity Palmer, 2001. The Quebrada Máquina is a small, montane stream on the seasonal Pacific slope of the Tilarán Mountain Range. The dam on the Quebrada Máquina in Monteverde, Costa Rica was built for water collection in 2004. Several months after construction, Rancourt 2004 studied the rainy sea son substrate composition and macroinvertebrate diversity as functions of distance from the dam. He found that sites closest to the dam exhibited decreased numbers of macroinvertebrate individuals, and significantly more sand directly upstream of the dam. As absolute distance from the dam increased, so did macroinvertebrate order richness diversity H . Additionally, as the relative percentage of sand as substrate RPSS increased, macroinvertebrate diversity and order richness decreased significantl y. Rancourt s study implicates the dam as the cause of a reduction in habitat heterogeneity and thus, a local decrease in macroinvertebrate diversity. This study examines ongoing change in substrate composition, macroinvertebrate diversity and temperatu re a new parameter both above and below the dam. Temperature is examined because dams alter temperature in rivers because reduced flow at the upstream reservoir causes water to heat. Downstream of the dam, water flow picks up and the turbulence and expos ure to air cool the water back to normal Allan, 1995. While

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3 few studies explicitly study macroinvertebrate community responses to temperature change, one can be certain that such communities do change. Water temperature is directly linked to the capaci ty of water to hold dissolved oxygen, so a shift in temperature means the alteration of at least two environmental parameters. Decreased dissolved oxygen negatively affects macroinvertebrate respiration, and without unique adaptations like flapping gills, many species cannot survive in deoxygenized environments Palmer, 2001. I expect to see changes in the physical environment of the dam, specifically in substrate composition and temperature that are congruent with Rancourt s findings but more exaggerat ed due to the effects of time and season. Lower water levels in the dry season should exaggerate the trends in substrate composition noted in Rancourt s study, as there will be less water in which to suspend sediment and small particles. Thus, I predict increased sediment and sand at sites closer to the dam. I also expect temperature to increase in the reservoir above the dam and decrease below the dam, as flow reduction causes temperature to increase Wetzel, 1983 and reintroduction of flow allows for reoxygenation and cooling by ambient air temperature Allan, 1995. As abiotic factors change, I expect them to influence biotic community structure and abundance. Sand is a poor substrate for most macroinvertebrates, which tend to be substrate specialist s, because of its instability and tendency to fill interstitial spaces which reduce habitat heterogeneity Erman and Lison, 1998; Stevens, 1996; Hyman, 2002. Given temperature s link to dissolved oxygen content, it will likely affect stream biota in the r eservoir above the dam. With substrate and temperature in mind, I expect to see a general decrease in macroinvertebrate diversity as distance from the dam decreases. However, the effects of habitat reduction cause the proliferation of species able to ada pt, at the expense of those not equipped to deal with changes, so I expect to see elevated levels of certain taxa in contrast to the decrease of most others Wood and Armitage, 1997. Results of this study will be important to understanding the Quebrada M áquina s continued response to the dam, and may be useful in suggesting conservation strategies for the stream. This study s findings can also enrich the literature on small stream ecology and may be useful for gaining insights into the effects of dams on tropical montane streams in general. Lastly, studies on small streams and dams are much more easily conducted than their equivalents on large dams on large rivers simply due to scale. Results from this study that can be scaled up are thus doubly impo rtant because they save effort and funds required to study large rivers their dams. MATERIALS AND METHODS This study was conducted on a 100 m section of the Quebrada Máquina, spanning the dam built there, in Lower Montane Wet Forest in Monteverde, Costa Ri ca near the Estación Biológica de Monteverde. The dam measures three meters wide, 1.5 m high and 0.3 m deep Rancourt, 2004. Macroinvertebrates were collected between April 8 and May 4, 2006 from 9:30 to 11:00 am. Sample sites were chosen using a me asuring tape and marked with flagging tape. Starting at the dam, every five meters was marked for 50 m above and 50 m below the dam, resulting in a total of 20 sample sites. At each site, macroinvertebrate samples, relative substrate composition and tempe rature data were taken. In order to obtain representative samples of

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4 macroinvertebrates, benthic material was kicked up for two minutes and collected in a kicknet held downstream, following the procedure outlined in Mitchell and Stapp 1995. Contents of the kicknet were then transferred to plastic containers and 95% ethanol was added to preserve samples until identification. Macroinvertebrate samples were collected on four consecutive days, five samples per day, beginning at 50 m upstream of the dam and working sequentially down to 50 m downstream. When all samples had been collected, 12 consecutive days were spent identifying the macroinvertebrates at the Estación Biológica de Monteverde. Using a dissecting scope and How to Know the Aquatic Insects L ehmkuhl, 1979 all macroinvertebrates were classified to order and morphospecies levels. When possible, identifications were made to family level. Morphospecies is a manner of classification that groups insects of similar phenotypical characteristics. Morphospecies level is important in measuring diversity because it focuses on different physical attributes of species found, which is often a better indicator of what kinds of species an environment can sustain. Relative substrate composition was measured for each site on two consecutive days. Substrate was classified as sand grain diameter < 2 mm, small rock diameter 2 mm 3cm, medium rock diameter 3 8 cm, large rock diameter > 8 cm wood and leaf debris, or sediment a loss , easily dislodged cover ing of dirt. An 8.5 by 11 inch piece of paper was held just above the water s surface and the substrate most abundant in the area beneath it was recorded for that area i.e. if the area was mostly but not necessarily entirely comprised of sand, the 8.5 x 11 inch area was considered to have a sand substrate. This was repeated until the entire area of the site was covered, and from this data each substrate s relative abundance was calculated. Temperature was measured three times at each site on three cons ecutive days in order to calculate a mean value. Using a thermometer, temperature was gauged in the center of each site, just above the benthic material level, as it is that temperature that most likely affects the macroinvertebrates most of them benthic . Shannon Weiner diversity indices were calculated for macroinvertebrate and substrate data. Data were analyzed using polynomial regressions, Mann Whitney U Tests and one one sample t test. RESULTS Community Richness A total of 1592 macroinvertebrates were collected and classified 797 individuals from upstream and 795 from downstream of the dam. By far the most common order was Diptera, with 1083 individuals, 1072 of which were Diptera pupae. The second most abundant order was Coleoptera, with 377 ind ividuals collected. Morphospecies I had the most recorded individuals with 1119 total; 500 upstream and 619 downstream from the dam. Morphospecies A had the second greatest abundance with 326 individuals; 203 above the dam and 123 below Figure 1a. The number of individuals per site did not change significantly as distance to dam decreased Figure 2a, R 2 = 0.09, P value = 0.43, n = 20. Number of orders and morphospecies per site increased significantly as distance from the dam increased Figures 2b an d 2c; R 2 = 0.51 and 0.40, respectively, P values = 0.002 and 0.01, respectively, n =

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5 20. The average number of individuals above and below were compared and no significant difference was found. The average order richness between above and below the dam also did not differ significantly. The average Morphospecies number also did not differ significantly between sites above and below the dam. Table 1 Environmental diversity Diversity of substrate, measured as a Shannon Weiner index H , increased signif icantly as distance from the dam increased Figure 3b, R 2 = 0.16, P value = 0.04. As distance from the dam increased, the relative percentage of sand as a substrate RPSS increased significantly Figure 3c, R 2 = 0.66, P value = 0.0001. Conversely, as distance from the dam increased, the relative percentage of sediment as a substrate decreased significantly Figure 3d, R 2 = 0.57, P value < 0.0001; Figure 4. Average diversity of substrate was 0.64 upstream of the dam and 0.80 downstream. Above the dam RPSS was 41.6% versus 12.6% below. Percentage of sediment as substrate averaged 30.2% upstream and 41.0% downstream of the dam. None of these differences in these abiotic factors were significantly different Table 2. Temperature increased significa ntly from upstream to downstream Figure 3a, R 2 = 0.89, P value <0.0001. Average temperature above the da m was 15.7 ÚC and below the dam was 16.0 ÚC. When temperatures above the dam were compared with temperatures below the dam, a significant difference was found Table 2. Twenty five meters downstream of the dam, water from the dam s storage container is re introduced to the stream via two pipes. Water temperature at this site was found to be significantly higher than the temperatures of all other sites Table 3. DISCUSSION The dam on the Quebrada Máquina is clearly affecting the physical environment of the stream, and this in turn impacts macroinvertebrate communities. Not only is sand cover more extensive both above and below the dam than was observed in Rancourt s 2004 study, sediment has become an element of the landscape of macroinvertebrate habita ts since then. Sediment negatively affects benthic macroinvertebrates in four ways. First, it changes substrate composition, and decreases the amount of suitable habitat for the majority of these organisms Erman and Ligon, 1998. Second, it reduces the amount of oxygen dissolvable in the water, decreasing respiration Lemley, 1982. Third, it hinders filter feeding and reduces the availability of prey Cline, 1982. Fourth, it obstructs migration W ood and Armitage, 1997. These changes affects all b enthic macroinvertebrates, decreasing the abundance and diversity of most taxa, but increasing a select few Wood and Armitage, 1997. In this case, the select few were the Dipteran pupae that comprised over two thirds of individuals collected. These h eadless, legless cocoons and their larva counterparts are often used as indicators of poor water quality so it makes sense that they are surviving in high abundances in the less than optimal conditions above and below the dam Allan, 1995. It is possibl e that the current substrate composition of the stream is a function of season as much as it is a result of the dam, in which case, when the rains come sediment will be washed away and conditions will return to being more like those found in

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6 Rancourt s stu dy, only to experience sediment buildup again next dry season 2004. Sedimentation varies with season, drought and other phenomena that influence water flow, so macroinvertebrates are equipped to endure pulses of high sediment suspension and deposition Wood and Armitage, 1997. However, if the high sedimentation close to the dam is more a function of the dam itself than the dry season in which this study was conducted, the sediment is here not only to stay, but also to increase. The low water flow and high sediment composition for the first 25 m downstream of the dam suggest that the latter, less optimistic possibility is probably more likely. The dam completely halts the flow of water below it, causing a relatively stagnant pool characterized by high sediment deposition from zero to 25 m downstream. Unless the dam overflows there will be nothing to establish flow in this area, and sediment will only build up. If this is the case, Diptera pupae will likely only increase in relative abundance, causing a proliferation of adult Dipterans and altering the assembly of the Quebrada Máquina community. The increasing temperature gradient from 50 m above the dam through 50 m below it is also an important factor to consider when contemplating the fate of biodive rsity in the Quebrada Máquina. As hypothesized, temperature does increase in the upstream reservoir created by the dam. An unexpected result was the continued heating of the stream below the dam. This was traced to the water storage tank where water cor ralled by the dam is sequestered. Excess water from the tank is carried back to the stream in two PVC pipes that discharge a constant flow of water at 25 m below the dam. While water sits in the storage tank it is heated, presumably by ambient air temper ature, sun and the insulating effects of the concrete tank. The temperature of the storage tank water was 16.4 ÚC when measured on a day that the maximum stream site temperature was 16.2 ÚC. It is this reintroduction of warmed tank water that creates the s ignificant peak temperature at 25 m Figure 3a. The effects of temperature on macroinvertebrate community richness and assembly have not been well documented, but increased temperature reduces dissolved oxygen concentrations, which lowers respiratory ab ility, decreasing the abundances of most macroinvertebrates Lemly, 1982. Other than disrupting the temperature patterns usually established in the presence of a dam, the storage tank coupled with the dynamic reintroduction of warmed water at 25 m downst ream also affects substrate composition. At 25 m downstream the reintroduction is very turbulent water falls half a meter from the pipes to the surface of the stream, creating a waterfall like effect, churning up the relatively stagnant water coming downs tream and dispelling sediment. The instant change from 90% sediment to 100% small rock, compounded by turbulent water probably acts as a barrier to many species, and may further inhibit some species migratory patterns. At first glance the benthic level of the Quebrada Máquina does not look like it harbors great diversity. Upon kicking up this layer, however, one finds a community teeming with macroinvertebrates in all stages of life. The former perspective informs too many decisions regarding stream co nservation or a lack thereof. The macroinvertebrates collected in this study were all well suited for their environments. Under the microscope these organisms could easily be taken for twigs, rocks or even flowers to the untrained eye, suggesting an ev olutionary premium on crypsis that has developed over time. By altering macroinvertebrates environments, dams make these organisms vulnerable to a number of dangers, including predation. Benthic macroinvertebrates are at the base of stream ecosystem foo d chains that include both aquatic and terrestrial organisms. Losses in

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7 biodiversity or shifts in community assemblage on such a fundamental trophic level affect the entire ecosystem, which includes numerous endangered Anuran species Masters, 2004. Tw o important aspects of this study can be generalized for dams of all sizes. The deleterious effects on temperature caused by the reservoir formed downstream of the dam by the dam s cessation of flow until the 25 th meter is something that could affect a st ream or river of any size in any environment. It is important that if a dam completely stops the flow of water between upstream and downstream portions of the river, that water be reintroduced downstream as close to the dam as possible. In a larger scale prototype of the Quebrada Máquina dam the effects of the 25 m stagnant pool might be more devastating to macroinvertebrate populations because, assuming larger rivers have greater, faster flow, the contrast would be more abrupt and macroinvertebrates migh t not be equipped to cope with such drastic changes in environment over such small distances. Another generalization that can come from this study is the synergy of negative effects of dams on aquatic ecosystems. In Rancourt s 2004 study one and a hal f years before this one there was no mention of sediment in the substrate of the Quebrada Máquina. Today, sediment dominates substrate composition for 15 m above and 20 m below the dam. Studies of small and large dams alike in both tropical and temperate zones have pointed to the accumulation of sediment over time due to reduced flow regime Allan, 1995; Mitchell, 1995; Sand Jensen, 2001. This sedimentation shortens the life of the dam, further slows the flow of water, devastates macroinvertebrate commu nity function and has repercussions up the food chain Allan, 1995. Dams should only be built with the stipulation that natural watersheds around the river or stream be maintained, so that excess sedimentation due to erosion does not affect this cycle. No river is immune to the abiotic environmental changes that come with dam construction, and these changes then affect biotic community richness, assembly and function. While not every facet of this study can be related to stream dam situations elsewhere, there are important conservation implications based on its results that can be applied universally. ACKNOWLEDGEMENTS Most profound thanks to Dr. Karen Masters for advising the design, execution and analysis of this experiment. Without her sound and timely input, endless patience and brilliant insight this project would not have been possib le. I am grateful to Maria Jos é for showing me the actual Quebrada Máquina dam on that first morning when I set out to collect insects without knowing where I was headed. To Maria again and the resplendent Ollie Hyman: mil gracias for providing me with research equipment, statistically savvy advice and continued support all semester. Thank you to Dr. Alan Masters for troubleshooting early on and to Javier Ménde z for help with translating. Finally, undying gratitude to my faithful companions in the nerdery notably Kristen Kennedy Becklund for putting up with the stench of my benthic samples and for sacrificing if involuntarily numerous brain cells in the nam e of stream ecology. LITERATURE CITED Allan, J.D. 1995. Stream Ecology: Structure and function of running waters . Alden Press, Oxford, Great Britain. Benke, A.C. 1990. A perspective on America s vanishing streams . Journal of the North American Benth ological Society ., 9, 77 88.

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8 Cline, L.D. R.A. Short, J.V. Ward. 1982. The influence of highway construction on the macroinvertebrates and epilithic algae of a high mountain stream. Hydrobiologia, Vol 96, No 2: 149 159. Erman, D.C., F.K Lison. 1998. Effe cts of discharge fluctuation and the addition of fine sediment on stream fish an d macroinvertebrate rates below a water filtration facility. Environmental management . Vol 12: 85 97. Hyman, O.J. 2002. Substrate effects on macroinvertebrate composition and guild structure. In: CIEE Fall Tropical Ecology and Conservation. Lehmkuhl, D.M. 1979. How to know the aquatic insects . Wm. C. Brown Company, Dubuque, Iowa. Lemly, A.D. 1982. Modification of benthic insect communities in polluted streams: effect s of sedimentation and nutrient environment. Hydrobiologia Vol 87: 229 245. Masters, K.L. 2004. Environmental impacts of dams and reduced flow on the Quebradas Máquina and Cuecha of Monteverde. Monteverde Streams Committee. Mitchell, M.K and W.B. Stapp . 1995. Field manual for water quality monitoring . Thomas Shore, Inc. Dexter, Michigan. pp. 27 33, 119 127. Palmer, M.A. 2001. Invertebrates, Freshwater, Overview. In: Encyclopedia of Biodiversity . Vol. 3. Editor: Simon Asher Levin. Academic Press : San Diego. pp. 531 542. Rancourt, J.R. 2004. Macroinvertebrate communities and streambed substrates of a dammed stream in Monteverde, Costa Rica. In: CIEE Fall Tropical Ecology and Conservation:179 189. Sand Jensen, K. 2001. Freshwater Ecosystems, Human Impact On. In: Encyclopedia of Biodiversity . Vol. 3. Editor: Simon Asher Levin. Academic Press: San Diego. pp. 93 94. Stevens, S.E. 1996. Variations in microhabitat diversity of freshwater macroinvertebrates: a test of the Intermediate Distu rbance Hypothesis . In: UCEAP Monteverde Tropical Biology Program: 109 116. Vitousek, P.M., H.A. Mooney, J. Lubchenco, J.M. Melillo. 1997. Human domination of Earth s ecosystems. Science . Vol 277: 494 499. Whiles, M.R., K.R.Lips, C.M. Pringle. 2006 . The effects of amphibian population declines on the structure and function of Neotropical stream ecosystems. Frontiers in ecology and the environment . Vol 4, No. 1: 27 34. Wood, P.J., P.D. Armitage. 1997. Biological effects of fine sediment in the lot ic environment. E nvironmental Management . Vol 21, No. 2: 203 217.

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9 FIGURE 1a. Abundance of different morphospecies. Number of individuals transformed logarithmically in order to show relative abundance of less represented mor phospecies. Morphospecies found below the dam were always found above the dam. Morphospecies G was unique to sites above the dam. Morphospecies I is dominated by Diptera pupae. Figure 1b. Relative percentage of morphospecies I as compared with all other morphospecies. Morphospecies I is comprised of Diptera pupae and Hymenoptera larvae, but Diptera pupae is overwhelmingly more abundant. 0 0.5 1 1.5 2 2.5 3 A B C D E G I J K Log number of individuals Morphospecies above dam below dam 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Relative percentage of morphospecies Distance from dam m non-morphospecies I hymenoptera larvae diptera pupae

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10 A B C F IGURE 2. Polynomial regressions of A number of individuals, B number of orders and C number of morphospecies as distance from dam varies. Number of orders and morphospecies increase y = 0.0094 x 2 0.307 x + 70.698 0 20 40 60 80 100 120 140 160 180 200 -50 -40 -30 -20 -10 0 10 20 30 40 50 Number of individuals Distance from dam m y = 0.0011 x 2 + 0.026 x + 3.378 0 1 2 3 4 5 6 7 8 9 -50 -40 -30 -20 -10 0 10 20 30 40 50 Number of Orders Distance from dam m y = 0.0009 x 2 + 0.0148 x + 3.937 0 1 2 3 4 5 6 7 8 9 -50 -40 -30 -20 -10 0 10 20 30 40 50 Number of morphospecies Distance from dam m

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11 significantly as distance from dam increases. Number of individuals shows the same trend, but does not change significantly as distance from dam increases. Negative values on x axis indicate distances downstream from dam, positive values indicate upstream distances. White square points represent values at 25 m downstream , where diverted water is reintroduced to the stream via pipes. TABLE 1. Different measures of macroinvertebrate diversity above versus below the dam: Quantitative results of Mann Whitney U Test. U Prime Tied P Value n Ave rage above Average below Individuals 52.0 0.88 20 79.9 79.5 Orders 71.5 0.10 20 5.1 3.7 Morphospecies 64.0 0.27 20 5.2 4.5 a b c d ________________________________________________________________________ FIGURE 3. Polynomial regressions of abiotic change as distance from dam varies. a average temperature b diversity of substrate, c sand percentage of substrate and d sediment p ercentage of substrate versus distance from dam. All are statistically significant. Temperature increases from upstream to downstream, diversity of substrate y = 0.0001 x 2 0.0064 x + 15.956 15.2 15.3 15.4 15.5 15.6 15.7 15.8 15.9 16 16.1 16.2 16.3 -50 -40 -30 -20 -10 0 10 20 30 40 50 Average temperature degrees C Distance from dam m y = 0.0002 x 2 0.002 x + 0.5256 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 -60 -40 -20 0 20 40 60 H' substrate Distance from dam m y = 0.0289 x 2 + 0.5255 x 0.7425 0 10 20 30 40 50 60 70 80 90 100 -50 -40 -30 -20 -10 0 10 20 30 40 50 Percent sand as substrate % Distance from dam m y = 0.0422 x 2 0.1187 x + 76.239 0 10 20 30 40 50 60 70 80 90 100 -50 -40 -30 -20 -10 0 10 20 30 40 50 Percentage sediment as substrate % Distance from dam m

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12 and relative sand percentage increase as distance from the dam increases, and relative percentag e of sediment decreases as distance from dam increases. Negative values on x axis indicate distances downstream from dam, positive values indicate upstream distances. White square points represent values at 25 m downstream, where diverted water is reintro duced to the stream via pipes. TABLE 2. The abiotic environment above and below the dam . Quantitative results of Mann Whitney U Test. U Prime Tied P Value n Average above Average below Average temperature 98.0 < 0.0001 20 15.7 Ú C 16.0 Ú C Substrate diversity H 59.0 .49 20 0.64 0.80 Relative sand as substrate 71.5 .09 20 41.6% 12.6% Relative sediment as substrate 52.5 .84 20 30.2% 41.0% TABLE 3. Results of a one sample t test, demonstrating that water is significantly higher in temperature when it is reintroduced to the Quebrada Máquina at 25 m downstream of the dam 16.2 ÚC. Hypothesized difference t value P value 16.2 ÚC as compared with the 19 other temperatures 0 2.2 0.04 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 50 45 40 35 30 25 20 15 10 5 -5 -10 -15 -20 -25 -30 -35 -40 -45 -50 Relative fraction of substrate composition Distance from dam m Sand Sediment Small Rock Large Rock Leaf Debris Boulders

PAGE 13

13 FIGURE 4. Substrate composition at all 20 sites. APPENDIX 1: The relative abun dance and descriptions of aquatic macroinvertebrates found at 10 sites above and 10 sites below the dam on the Quebrada Máquina in Monteverde, Costa Rica. Guide to morphospecies A worm shaped, has legs B round, flat, hard shell; large eyes C small beetles, dark in color D shrimps and crabs E elongate, cricket like, segmented bodies G spider like in appearance I featureless, cocoon shaped J flying terrestrial insects K water striders, found on surface Distance from dam Orde r Family # Morpho species Comments 50 m upstream Coleoptera Helodidae 2 C Black beetle with red accents. 50 m upstream Diptera 2 J Terrestrial. 50 m upstream Hemiptera Corixidae 1 C 50 m upstream Coleoptera Psephenidae larvae 2 B Big red eyes on shel l. 50 m upstream Ephemeroptera Oligoneuriidae 1 E 50 m upstream Collembola Sminthuridae 1 G 50 m upstream Hymenoptera 3 J Terrestrial wasps. 50 m upstream Coleoptera Halipidae 1 C 50 m upstream Ephemeroptera Baetiscidae nymph 2 E Large, brown, dar k eyes, nostril spots, tail severed, long antennae. 50 m upstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 12 A Yellow worm like with 3 pairs of true legs, lots of

PAGE 14

14 pseudolegs. 50 m upstream Odonata Libellulidae 2 J Dragonflies. Brown. P urple with red eyes. Many segments. 50 m upstream Crustacea 1 D Shrimp. 50 m upstream Diptera 1 J Terrestrial fly. 45 m upstream Choleoptera Ptilodactylidae or Elmidae larvae or cocoon 12 A 45 m upstream Hemiptera Naucoridae 5 B Creeping water bug s . 45 m upstream Choleoptera Helodidae 3 C 45 m upstream Crustacea 2 D Large crab, speckled brown body. 45 m upstream Diptera pupae 19 I 45 m upstream Crustacea Amphipoda 1 D White ethereal shrimp. 40 m upstream Diptera pupae 37 I

PAGE 15

15 40 m upstr eam Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 20 A 40 m upstream Coleoptera Helodidae 3 C 40 m upstream Crustacea Amphipoda 2 D 40 m upstream Hymenoptera larvae 8 I. Tiny white crescent cocoon. 40 m upstream Diptera Psychodidae 1 J 4 0 m upstream Ephemeroptera Baetiscidae nymph 1 E 40 m upstream Hemiptera Naucoridae 1 B creeping water bugs 35 m upstream Hymenoptera larvae 33 I 35 m upstream Diptera pupae 75 I 35 m upstream Diptera Psychodidae 5 J 35 m upstream Coleoptera P tilodactylidae or Elmidae larvae or cocoon 46 A 35 m upstream Odonata 2 J 35 m upstream Odonata Libellulidae 1 J 35 m upstream Ephemeroptera Baetiscidae nymph 1 E 35 m upstream Hemiptera Naucoridae 2 B 35 m upstream Hymenoptera 2 J Terrestrial bee. 35 m upstream Collembola Sminthuridae 1 G Tiny, peach colored spider shaped. 35 m upstream Hemiptera nymph Veliidae 4 K Cig red eyes, brown body, no wings, 8 pac on back in brown. Riffle bugs, broad shouldered water striders 35 m upstream Odonat a larvae Libellulidae 1 E Large, red pink, cricket like. 35 m upstream Coleoptera Helodidae 1 C

PAGE 16

16 35 m upstream Ephemeroptera Tricorythidae nymph 1 E 35 m upstream Arachnida 1 G Yellow tan, tiny, floating, red and white eyes. Legwarmer hairs 35 m u pstream Coleoptera Psephenidae larvae 2 B 30 m upstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 14 A 30 m upstream Diptera pupae 55 I 30 m upstream Coleoptera Haliplidae 1 C Red belly. 3 segments. 30 m upstream Ephemeroptera Baetisci dae nymph 1 E 30 m upstream Hemiptera Naucoridae 2 B 30 m upstream Coleoptera Psephenidae larvae 4 B 30 m upstream Crustacea Amphipoda 1 D 30 m upstream Hymenoptera larvae 2 I 25 m upstream Diptera pupae 42 I 25 m upstream Coleoptera Ptilodac tylidae or Elmidae larvae or cocoon 16 A 25 m upstream Coleoptera Psephenidae larvae 1 B 25 m upstream Ephemeroptera nymph Neoephemeridae 1 E Yellow nymph with very long thin tail. 25 m upstream Odonata larvae Libellulidae 1 E 25 m upstream Crusta cea Amphipoda 1 D 20 m upstream Odonata larvae Libellulidae 3 E 20 m upstream Diptera pupae 43 I 20 m upstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 23 A 20 m upstream Hemiptera Naucoridae 2 B

PAGE 17

17 20 m upstream Ephemeroptera nymph Ne oephemeridae 5 E 20 m upstream Coleoptera Psephenidae larvae 2 B 20 m upstream Ephemeroptera Baetiscidae nymph 2 E 20 m upstream Coleoptera Haliplidae 1 15 m upstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 16 A 15 m upstream Diptera pupae 34 I 15 m upstream Odonata larvae Libellulidae 1 E 15 m upstream Diptera Psychodidae 2 J 10 m upstream Diptera pupae 52 I 10 m upstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 27 A 10 m upstream Crustacea Amphipoda 1 D 10 m upstream Coleoptera Psephenidae larvae 2 B 5 m upstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 17 A 5 m upstream Diptera pupae 96 I 5 m upstream Hymenoptera larvae 4 I 5 m downstream Diptera pupae 26 I 5 m downstream Coleoptera Pt ilodactylidae or Elmidae larvae or cocoon 7 A 5 m downstream Coleoptera Haliplidae 1 5 m downstream Coleoptera Psephenidae larvae 1 B 10 m downstream Ephemeroptera nymph Neoephemeridae 1 E 10 m downstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 8 A 10 m downstream Diptera pupae 14 I

PAGE 18

18 10 m downstream Odonata larvae Libellulidae 1 E 10 m downstream Coleoptera Haliplidae 1 C 15 m downstream15 m downstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 21 A 15 m downstream Diptera pupae 11 I 15 m downstream Odonata Libellulidae 2 J 15 m downstream Ephemeroptera Baetiscidae nymph 2 E 15 m downstream Odonata larvae Libellulidae 1 E 15 m downstream Coleoptera Psephenidae larvae 1 B 20 m downstream Diptera pupae 68 I 2 0 m downstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 18 A 25 m downstream Diptera pupae 31 I 25 m downstream Hemiptera Naucoridae 1 B 25 m downstream Coleoptera Psephenidae larvae 1 B 25 m downstream Coleoptera Ptilodactylidae or El midae larvae or cocoon 4 A 25 m downstream Hemiptera nymph Veliidae 7 K 30 m downstream Odonata larvae Libellulidae 2 E 30 m downstream Ephemeroptera Baetiscidae nymph 2 E 30 m downstream Odonata Libellulidae 1 J 30 m downstream Diptera pupae 112 I 30 m downstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 16 A 30 m downstream Coleoptera Psephenidae larvae 1 B

PAGE 19

19 35 m downstream Coleoptera Psephenidae larvae 3 B 35 m downstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 19 A 35 m downstream Diptera pupae 89 I 35 m downstream Hymenoptera 1 J 35 m downstream Hemiptera nymph Veliidae 7 K 35 m downstream Crustacea Amphipoda 2 D 40 m downstream Diptera pupae 64 I 40 m downstream Coleoptera Ptilodactylidae or Elmida e larvae or cocoon 10 A 40 m downstream Hemiptera nymph Veliidae 2 K 40 m downstream Hemiptera Naucoridae 1 B 45 m downstream Hemiptera nymph Veliidae 3 K 45 m downstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 11 A 45 m downstream Diptera pupae 108 I 45 m downstream Odonata larvae Libellulidae 1 E 45 m downstream Odonata Libellulidae 2 J 45 m downstream Crustacea Amphipoda 1 D 50 m downstream Diptera pupae 96 I 50 m downstream Odonata larvae Libellulidae 1 E 50 m downstream Hemiptera nymph Veliidae 2 K

PAGE 20

20 50 m downstream Coleoptera Ptilodactylidae or Elmidae larvae or cocoon 9 A 50 m downstream Hemiptera Naucoridae 1 B TOTALS 9 16 1592 10


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