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The San Luis river continuum: a look at the chemical and biological changes along a longitudinal pristine river gradient

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Title:
The San Luis river continuum: a look at the chemical and biological changes along a longitudinal pristine river gradient
Translated Title:
La continuidad del río San Luis: Una mirada a los cambios químicos y biológicos a lo largo de un gradiente longitudinal del río ( )
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Book
Language:
English
Creator:
Hamley, Kit
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Subjects

Subjects / Keywords:
River continuum concept   ( lcsh )
Aquatic insects--Costa Rica--Puntarenas--San Luis   ( lcsh )
Concepto del río continuo
Insectos acuáticos
Tropical Ecology 2009
Biotic assemblages
Longitudinal gradient
San Luis River (Costa Rica)
Ecología Tropical 2009
Asociaciones bióticas
Gradiente longitudinal
Río San Luis (Costa Rica)
Genre:
Reports   ( lcsh )
Reports

Notes

Abstract:
From start to finish, physical changes along a river continuum create a natural longitudinal gradient to which biotic communities respond. This biotic response to natural physical change is a fundamental pattern of river ecology and is generally called The River Continuum Concept. The purpose of this study was to look at changes in water quality and aquatic insect communities along a pristine river continuum. Data was collected along a 1-kilometer series of 11 sites along the San Luis River in San Luis, Costa Rica. As expected, water quality did not change along the 1-kilometer reach. Overall percent abundances of insect Orders were different for each site. Three regions were created within the 1-kilometer continuum based on similarities in Shannon-Weiner values. Comparisons of these regions showed that percent composition of insect Orders fluctuate between the three regions. Water quality values were consistent over the entire continuum, therefore changes in biotic assemblages due to water degradation can be ruled out. This means that the changes observed in biotic assemblages were due to changes created by a natural longitudinal gradient.
Abstract:
De principio a fin, cambios físicos a lo largo de un rio continuo crea un gradiente longitudinal al cual las comunidades abióticas responden. Estos cambios bióticos son respuestas naturales a los cambios físicos y fundamentales para la ecología del rio y que generalmente se llama Concepto de Continuidad Riparia. El propósito de este estudio fue observar los cambios en la calidad del agua y las comunidades de insectos acuáticos a lo largo de un rio.
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Text in English.
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University of South Florida Library
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usfldc doi - M39-00109
usfldc handle - m39.109
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Hamley 1 The San Luis River Continuum: A look at the chemical and biological changes along a longitudinal pristine river gradient Kit Hamley Department of Biology, Bowdoin College ABSTRACT From start to finish, physical changes along a river continuum create a natural longitudinal gradient to which biotic communities respond. This biotic response to natural physical change is a fundamental pattern of river ecology and is generally called The River Continuum Concept. The purpose of this study was to look at chang es in water quality and aquatic insect communities along a pristine river continuum. Data was collected along a 1 kilometer series of 11 sites along the San Luis River in San Luis, Costa Rica. As expected, water quality did not change along the 1 kilometer reach. Overall percent abundances of insect Orders were different for each site. Three regions were created within the 1 kilometer continuum based on similarities in Shannon Weiner values. Comparisons of these regions showed that percent composition of in sect Orders fluctuate between the three regions. Water quality values were consistent over the entire continuum, therefore changes in biotic assemblages due to water degradation can be ruled out. This means that the changes observed in biotic assemblages w ere due to changes created by a natural longitudinal gradient. RESUMEN De principio a fin, cambios f ’sicos a travŽs de un continuo en los r’os crea un gradiente longitudinal al cual las comunidades abi—ticas responden. Estos cambios bi—ticos son respuest as naturales a cambios f’sicos es fundamŽntela para la ecolog’a del r’o y es denominado Concepto de Continuidad Riparia. El prop—sito de este estudio fue observar los cambios en la calidad de agua y las comunidades de insectos acu‡ticos a lo largo de un r ’o. Los datos se colectaron en 11 sitios a lo largo de 1 kil—metro en el R’o San Luis, San Luis, Costa Rica. Como se esperaba la calidad de agua no cambia a lo largo de este kilometro. Sin embargo la abundancia de ordenes de insectos fueron diferentes p ara cada sitio. Tres regiones fueron creadas a lo largo de este kilometro basadas en similitudes del ’ndice Shannon Weiner. La calidad del agua fueron consistentes a lo largo de todo el continuo, sin embargo cambios en las comunidades abi—ticas pueden su ceder. Esto significa que cambios en las comunidades abi—ticas se deben a cambios naturales en el gradiente longitudinal. INTRODUCTION Beginning at the source of a river and continuing to the mouth, physical variables within a river system create a long itudinal gradient of conditions that result in biotic changes within constituent communities (Harding et al ., 1999; Montgomery, 1999). The shifting of biotic communities in response to changes along a longitudinal river gradient is a fundamental pattern of river ecology (Vannote et al. 1980; 1983; Naiman et al. 1987). This pattern has been generally accepted and is called The River Continuum Concept (Vannote et al. 1980). The River Continuum Concept envisions intricately linked longitudinal communities w here the upstream ecosystem processes influence those that

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Hamley 2 take place downstream (Naiman et al. 1987). With natural longitudinal changes in geomorphology occurring, benthic assemblages undergo compositional as well as structural changes (Vannote et al. 1 980; 1983; Naiman et al. 1987; Montgomery, 1999). An example of structural change may include variations in community diversity over the river continuum, resulting in the establishment of moderately diverse communities occurring at the headwaters, highly diverse communities in the middle reaches and moderately diverse communities close to the mouth (Vannote et al. 1980). Similarly, changes in river size may have affects on aquatic species assemblages as well. Moving from headwaters down the river continuum the composition of Orders becomes less similar to those at the headwater site and more similar to those seen at larger river sites (Bruns et al. 1982). For example, smaller headwater rivers are often strongly influenced by surrounding vegetation, which contributes detritus to the system and provides shading, thereby decreasing autotrophic production (Vannote et al. 1980). In general, a river system's biotic composition and structure undergoes linear changes along a natural gradient in response to natural variations in stream morphology (Magdych, 1984), and it is important to understand and take into account these natural changes when studying river processes (Minsall, 1988). The objective of the present study was to look at the changes in aquatic insect communities and water quality along a longitudinal stretch of a small pristine river. Due to the pristine nature of the reach of river under examination, it is assumed that water quality will not degrade but will remain relatively constant along the entire gradient. However, based on the River Continuum Concept, biotic communities will change along the stream gradient due to natural longitudinal changes in geomorphology. MATERIALS AND METHODS Study Site This study was conducted during the end of the dry season, mid April to mid May in Monteverde, Costa Rica. The sites where data collection occurred were all located within the Monteverde Cloud Forest Reserve, beginning at the San Luis Waterfall and continuing every 100 meters downstream for 1 km and ending at the edge of the Monteverde Cloud Forest Reserve. Elevation remained relatively constant for the entire reach. In total, data was collected from 11 sites. All sites were sampled between 10 AM and 4 PM. Water Quality For each site water samples were co llected from fast moving water and analyzed within 24 hours after collection. Samples were not taken from slow moving sites. The water samples were stored at 4 degrees Celsius when not in use. Using a LaMotte Smartcolorimeter, Nitrate and Phosphorus tests were run for each site. Hydrion test strips were used to determine pH. Biotic Sampling Aquatic insect samples were collected from fast and slow moving water for each of the 11 sites. In each fast moving water site, 5 rocks of similar size were chosen and all of the aquatic insects from each rock were collected. For each slow moving water site, the

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Hamley 3 bottom sediment was agitated for 30 seconds while a strainer was placed downstream to collect dislodged insects. Insects were stored in vials of 95% ethanol and sorted. Identifications were then made to the Family level. The Shannon Weiner Index of Diversity was used to calculate and compare species diversity and evenness between adjacent site locations. RESULTS Water Quality Phosphate, Nitrate and pH water qua lity values show very few differences site to site and along the entire 1 km continuum (Fig. 1). Biotic Assemblages Shannon Weiner Values are similar along the river continuum for sites 1 3 (Upper), 4 6 (Middle), and 7 11 (Lower). Shannon Weiner Values w ere highest at the Middle sites and lowest at the Upper sites (Fig. 2). Sorensen values were generally increasing along the longitudinal gradient. The highest number of shared families was between sites 8 and 9. The lowest number of shared families was be tween sites 1 and 2 (Fig. 3). In looking at the overall percentages of Order abundance, the percent values for each Order change for every site and thus, composition of each site is different (Fig. 4). Ephemeroptera is overall the most abundant Order along the continuum. At its highest, Ephemeroptera composes 66% of both sites 1 and 2. As Ephemeroptera decreases from sites 2 6, Trichoptera increases. As Ephemeroptera increases from sites 6 9, Trichoptera decreases. Both Diptera and Ephemeroptera occurred at every site. There are no additional visible trends among the other Orders. Percent composition of insect Orders from Upper, Middle and Lower sites changes along the continuum (Fig. 5). Ephemeroptera percentages are highest at the Upper site, and lowest a t the Lower site. Diptera values had the same trend. The overall percentage of Trichoptera was highest at the Lower site and lowest at the Upper site. The other Orders did not show any trends between sites.

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Hamley 4 FIGURE 1. Phosphate (A), Nitrate (B) and pH (C) water quality parameters show very few fluctuations between sites and overall along a 1 kilometer pristine stretch of the San Luis River in San Luis, Costa Rica. FIGURE 2. Shannon Weiner Values were given to each combined fast and slow sample site along a 1 kilometer pristine stretch of the San Luis River in San Luis, Costa Rica. Figure 3. A Sorensen comparison of the amount of shared taxonomic families between adjacent sites along a pristine river continuum on the San Luis River in San Luis, Co sta

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Hamley 5 Rica. (0 100 represents the amount of shared species between sites 1 and 2; 100 200 represents sites 2 and 3, and so on.) FIGURE 4. Percent abundance of aquatic insect Orders for combined fast and slow sites along a 1 kilometer pristine stretch of t he San Luis River in San Luis, Costa Rica. FIGURE 5. Percent composition of Orders among Upper (A), Middle (B) and Lower (C) sites along a pristine river continuum on the San Luis River in San Luis, Costa Rica. DISCUSSION

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Hamley 6 There were differences i n Shannon Weiner values for each site along the longitudinal gradient (Figure 3). The lowest Shannon Weiner values were found at the first three sites along the continuum. Sites 4 6 had the highest values and more moderate values were found in the last fo ur sites. For this reason, sites 1 3 were grouped together to make the Upper region, sites 4 6 to make the Middle region and 7 11 to make the Lower region. A possible explanation regarding the formation of these 3 regions is based on shading and riparian i nputs. The first three sites in the Upper region are heavily shaded by tree cover and are also deeply cut into the mountain. Sites 4 6, in the Middle region, were shaded heavily by trees but were not as deeply cut into the mountain and subsequently had mor e sunlight. The Lower region was heavily influenced by landslides and thus received large amounts of sunlight and possibly was subject to changes in riparian inputs. Exposure to sun and changes in riparian inputs could possibly explain the trends between r egions (Vannote, 1980; Minshall, 1983; McTammany, 2003). Many headwater streams are heavily influenced by riparian vegetation, which reduces autotrophic production by shading and contributes large amounts of detritus (Vannote, 1980). This in turn causes ch anges in the biotic communities dependent on organic inputs or algal production. The Upper region, characterized by low species diversity), shared very few species between adjacent sites. Thus, in areas with fewer species, the chance of there being overla p in species composition decreases. Similarly, if there are a lot of species in two adjacent sites, the chance of them sharing species greatly increases. The data collected does not show the latter trend as clearly, though there are general increases in bo th the Sorensen and Shannon Weiner values for sites 4 11 Sites 8 and 9 shared the most species in common out of all adjacent sites. Generally speaking, there were definite changes in biotic community structure along the longitudinal gradient. In looking a t overall Order abundances, there are definite trends occurring between Orders. Ephemeroptera was present, and made up at least 20 percent of the abundance at every site. Similarly, Diptera was the only other Order to be present at every site along the con tinuum. Trichoptera was only absent from site 2 and appeared to have an interesting relationship with Ephemeroptera. When Ephemeroptera abundance was high, as in sites 1 and 2, Trichoptera abundance was low. As Ephemeroptera abundance went down from sites 2 6, Trichoptera abundances increased accordingly. Likewise, Ephemeroptera became more abundant from sites 6 9 and subsequently Trichoptera abundance went back down. It seems slightly unusual that this would occur because the feeding strategies of most Ep hemeroptera families were different than the feeding strategies of the Trichoptera families (Hawkins, 1981), thus perhaps they are competitors for space and when one is high in abundance, the other's fitness is reduced and it is not able to become as abund ant. The amount of inputs may have caused the fluctuations between Trichoptera and Ephemeroptera. Most of the Families within Ephemeroptera are collectors meaning they gather fine particulate organic matter from sediments (Vannote, 1980). The upper sites a nd lower sites where Ephemeroptera were high were characterized by steeper slopes and landslides, which could have been contributing more sediment to the stream body and adding to the availability of food for Ephemeroptera Families. When the surrounding sl opes were more stable, as they were at the middle sites, perhaps food was scarcer for collectors, therefore allowing Trichoptera to dominate.

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Hamley 7 There were differences in Shannon Weiner values for each site along the longitudinal gradient (Figure 3). The low est Shannon Weiner values were found at the first three sites along the continuum. Sites 4 6 had the highest values and more moderate values were found in the last four sites. For this reason, sites 1 3 were grouped together to make the Upper region, site s 4 6 to make the Middle region and 7 11 to make the Lower region. A possible explanation regarding the formation of these 3 regions is based on shading and riparian inputs. The first three sites in the Upper region are heavily shaded by tree cover and are also deeply cut into the mountain. Sites 4 6, in the Middle region, were shaded heavily by trees but were not as deeply cut into the mountain and subsequently had more sunlight. The Lower region was heavily influenced by landslides and thus received large amounts of sunlight and possibly was subject to changes in riparian inputs. Exposure to sun and changes in riparian inputs could possibly explain the trends between regions (Vannote, 1980; Minshall, 1983; McTammany, 2003). Many headwater streams are heavi ly influenced by riparian vegetation, which reduces autotrophic production by shading and contributes large amounts of detritus (Vannote, 1980). This in turn causes changes in the biotic communities dependent on organic inputs or algal production. The Upp er region, characterized by low species diversity), shared very few species between adjacent sites. Thus, in areas with fewer species, the chance of there being overlap in species composition decreases. Similarly, if there are a lot of species in two adjac ent sites, the chance of them sharing species greatly increases. The data collected does not show the latter trend as clearly, though there are general increases in both the Sorensen and Shannon Weiner values for sites 4 11 Sites 8 and 9 shared the most sp ecies in common out of all adjacent sites. The River Continuum Concept generally states that from source to mouth, the physical variables within a river system create a longitudinal gradient of conditions that in turn cause a continuum of changes to bioti c communities within the system (Vannote, 1980). There were no changes in water quality values, therefore, changes in biotic communities are likely not due to degradation of water quality. Similarly, elevation along the entire stream gradient also remained constant, so biotic changes would not have occurred due to elevation gain or loss. This leads to the conclusion that the biotic changes observed here were due to natural variations along the longitudinal river gradient. Natural changes in community struc ture are important to the functioning of the stream as a whole. Aquatic insects shift with changes in food resources as well as stream size (Vannote, 1980). The San Luis River showed natural changes in biotic communities along a continuum and could potenti ally acts a good model to compare polluted streams to. Therefore, having an understanding of these natural biotic changes along a river continuum will only further our knowledge about river systems. Flowing water systems are extremely diverse and complex b ut because our lives are so intricately tied to and dependent on them, they are extremely important to understand on a holistic level. ACKNOWLDEGEMENTS I would like to thank my advisor Anjali Kumar for all of her help throughout the duration of my proj ect. I would also like to thank Pablo Allen for his assistance in identifying my aquatic insects. I would also like to acknowledge Yimen Araya and Jose Carlos Calderon for helping me gather supplies and with other project logistics. Thanks also to my

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Hamley 8 estee med field assistant Laura Heil for her help collecting data. Lastly, thanks to Bowdoin College and my parents who made it possible for me to study in Costa Rica. LITERATURE CITED B RUNS D. A., W AYNE M INSHALL J. T. B ROCK C. E. C USHING K. W. C UMMINS R L. V ANNOTE 1982. Ordination of Functional Groups and Organic Matter Parameters from the Middle Fork of the Salmon River, Idaho. Freshwater Invertebrate Biology. 1: 2 12. H ARDING J .S., R.G. Y OUNG J.W. H AYES K.A. S HEARER AND J.D. S TARK 1999. Changes in agricultural intensity and river health along a river continuum. Freshwater Biology. 42: 345 357. H AWKINS C. P. AND J.R. S EDELL 1981. Functional Groups in Streams. Ecology. 62: 387 397. M AGDYCH W. P 1984. Salinity Stresses Along a Complex River Continu um: Effects on Mayfly (Ephemeroptera) Distributions. Ecological Society of America. 65: 1662 1672. M C T AMMANY J.R., W EBSTER E.F. B ENFIELD AND M.A. N EATROUR 2003. Longitudinal patterns of metabolism in a southern Appalachian river. The North American Be nthological Society. 22: 359 370. M ONTGOMERY D.R. 1999. Process Domains and the River Continuum. Journal of the American Water Resources Association. 35: 397 410. M INSHALL W.G., R.C. P ETERSEN K.W. C UMMINS T.L. B OTT J.R. S EDELL C.E. C USHING R.L. V AN NOTE 1983. Interbiome Comparison of Stream Ecosystem Dynamics. Ecological Monographs. 53: 2 25. M INSHALL G.W. 1988. Stream ecosystem theory: A global perspective. The North American Benthological Society. 7: 263 288. N AIMAN R.J., J.M. M ELILLO M.A. L OC K T.E. F ORD S.R. R EICE 1987. Longitudinal patterns of ecosystem processes and community structure in a subarctic river continuum. Ecology. 68: 1139 1156. V ANNOTE R.L., G.W. M INSHALL K.W. C UMMINS J.R. S EDELL C.E. C USHING 1980. The River Continuum C oncept. Can. J. Fish. Aquat. Sci. 37: 130 137.


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La continuidad del ro San Luis: Una mirada a los cambios qumicos y biolgicos a lo largo de un gradiente longitudinal del ro
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The San Luis river continuum: a look at the chemical and biological changes along a longitudinal pristine river gradient
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From start to finish, physical changes along a river continuum create a natural longitudinal gradient to which biotic communities respond. This biotic response to natural physical change is a fundamental pattern of river ecology and is generally called The River Continuum Concept. The purpose of this study was to look at changes in water quality and aquatic insect communities along a pristine river continuum. Data was collected along a 1-kilometer series of 11 sites along the San Luis River in San Luis, Costa Rica. As
expected, water quality did not change along the 1-kilometer reach. Overall percent abundances of insect Orders were different for each site. Three regions were created within the 1-kilometer continuum based on
similarities in Shannon-Weiner values. Comparisons of these regions showed that percent composition of insect Orders fluctuate between the three regions. Water quality values were consistent over the entire continuum, therefore changes in biotic assemblages due to water degradation can be ruled out. This means that the changes observed in biotic assemblages were due to changes created by a natural longitudinal gradient.
De principio a fin, cambios fsicos a lo largo de un rio continuo crea un gradiente longitudinal al cual las comunidades abiticas responden. Estos cambios biticos son respuestas naturales a los cambios fsicos y fundamentales para la ecologa del rio y que generalmente se llama Concepto de Continuidad Riparia. El propsito de este estudio fue observar los cambios en la calidad del agua y las comunidades de insectos acuticos a lo largo de un rio.
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River continuum concept
Aquatic insects--Costa Rica--Puntarenas--San Luis
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Concepto del ro continuo
Insectos acuticos
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Tropical Ecology 2009
Biotic assemblages
Longitudinal gradient
San Luis River (Costa Rica)
Ecologa Tropical 2009
Asociaciones biticas
Gradiente longitudinal
Ro San Luis (Costa Rica)
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Reports
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CIEE
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t Monteverde Institute : Tropical Ecology
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