A Preliminary Water Quality Study of the Rio Sierpe and Its Tributaries (Costa Rica) Prepared for the Blue Moon Foundation
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Photo: Rio San Juan (tributary to Rio Sierpe) by D. Arscott A Preliminary Water Quality Study of the Rio Sierpe and its tributaries (Costa Rica) Prepared for the Blue Moon Foundation Prepared by: David B. Arscott , William Eldridge, and Bernard W. Sweeney Submitted on 6 April 2010 970 Spencer Road, Avondale, PA 19311 USA Phone: 610‐268‐2153 www.stroudcenter.org Page i Stroud Water Research Center Report 2010001 WATER QUALITY IN THE RIO SIERPE WATERSHED 6 APRIL 2010 Table of Contents I. Introduction ...................................................................................................... 1 II. Study Sites and Methods ................................................................................... 3 A. Water Chemistry ............................................................................................. 4 B. Aquatic Macroinvertebrate Methods ............................................................. 5 C. Fish Methods .................................................................................................. 5 III. Results ............................................................................................................. 11 A. Sites by Geographic Relationships ................................................................ 11 B. Water Chemistry ........................................................................................... 11 C. Aquatic Macroinvertebrates ......................................................................... 17 D. Fish ............................................................................................................ 24 IV. Conclusions: Goals and Outcomes ................................................................ 37 V. Literature Cited ............................................................................................... 39 VI. Appendix 1: Site Photos ................................................................................ 41 VII. Appendix 2: Photographs of fish collected ................................................... 71 Page ii Stroud Water Research Center Report 2010001 WATER QUALITY IN THE RIO SIERPE WATERSHED 6 APRIL 2010 I. Introduction This report documents the results from a preliminary field study conducted by the Stroud Water Research Center in April 2009 in the Rio Sierpe watershed in southwest Costa Rica (Fig. 1). The field study was commissioned by the Blue Moon Foundation (Charlottesville, VA, USA) as part of their effort to help understand and protect valuable ecosystems. We conducted an initial scoping study that will guide the development of a more rigorous project to measure both the current state and future changes in the health of the stream network within the Rio Sierpe and nearby regions. Figure 1: Land use and study sites in the Rio Sierpe watershed, northwest Costa Rica. The Rio Sierpe is a medium sized river located in southwestern Costa Rica with mixed land uses throughout (Fig. 1) including native forest, agriculture (primarily palm oil plantations, rice production, banana plantations, shrimp farming, and livestock grazing). The lower reaches and estuary support one of the largest mangrove swamps (~270 km2) along the Pacific coastline of Latin America, the Térraba Sierpe National Wetlands (est. March 1994). This mangrove, in turn, supports an important recreational fishery and is economically important to the region. The mangrove swamp is a primary factor responsible for a large effort to establish a scalable and replicable framework for the integration of Technical, Institutional and Conceptual Solutions (TICOS) to promote its sustainable development (Azur Moulaert, University of Vermont, ‐ personal communication). The Rio Sierpe watershed has gradually undergone human development resulting in significant portions of the original old growth tropical forest being eliminated and replaced by agriculture and other human activities. Moreover, significant changes are expected in the near future due Page 1 Stroud Water Research Center Report 2010001 WATER QUALITY IN THE RIO SIERPE WATERSHED 6 APRIL 2010 to increased interest in aquaculture and the changing nature of agriculture in the region and urbanization associated with the possible expansion to service international flights at the airport at Palmar Sur, a small town whose suburbs extend into the Rio Sierpe watershed (Dan Janzen personal communication). These expected changes in the local economy and potentially in the environment result in a need to: (i) quantify current environmental conditions in streams and rivers of the Rio Sierpe watershed and mangrove swamp; (ii) determine relationships between stream water quality and land use; (iii) develop environmental monitoring tools and baseline physical, chemical, and biological data to track degradation and improvement in water quality over time; and (iv) engage and train local residents in the use of monitoring tools. The objective of this study was to survey stream chemical and biological (aquatic macroinvertebrates and fish) conditions throughout the Rio Sierpe watershed to determine the feasibility of conducting a larger scale effort to quantify water quality and develop protocols and community involvement in monitoring the health and integrity of the watershed. In April 2009, a one‐week expedition was conducted to: (i) rapidly assess chemical and biological quality of small, medium, and large streams/rivers in the watershed that represented the range of current landuses; (ii) assess the feasibility of establishing a 2‐3 year monitoring program to provide a quantitative baseline to firmly and accurately establish the current spatial and temporal status of water quality; and (iii) establish working relationships with individuals/institutions/ organizations/decision makers who are interested in, working with, or affected by water quality and who can help implement a water quality monitoring program and/or use it for purposes of local conservation, education, or economic well being of the community. Understanding the local and regional variability in stream water chemistry is a prerequisite for the determination of the impact of human activities on water quality. Human activities can result in subtle, but important, increases in the concentrations of ions and nutrients dissolved in stream water. For example, some human activities result in small increases in stream nitrate‐ nitrogen and inorganic phosphorus concentrations that can result in increased standing stock and growth rates of algae. Increased standing stock of algae can alter aquatic macro‐ invertebrate communities and change food type and availability for certain fish species. These subtle changes may ultimately result in altered fish community structure and a change in the type of fish available for human consumption or for recreational opportunities. Other types of human activities can result in the release of toxic chemicals into streams and more directly impact both fish and human health. Human activities can also result in the degradation and/or alteration of a streams physical habitat. For example, deforestation without re‐vegetation often results in increased delivery of fine sediments to a stream that can smother stream bed sediments thereby reducing hydrological exchange between surface and groundwater and affecting the interstitial habitat for both invertebrates and fish. For these reasons, a comprehensive stream monitoring program typically involves the quantification of chemical, physical, and biological attributes within a stream. Aquatic macroinvertebrate and fish communities are useful for assessing water and habitat quality and ecosystem structure and function in streams and have been used for this purpose for more than 100 years (Cairns and Pratt 1993). Benthic (i.e., bottom‐dwelling) macro‐ Page 2 Stroud Water Research Center Report 2010001 WATER QUALITY IN THE RIO SIERPE WATERSHED 6 APRIL 2010 invertebrates, in particular, are one of the most common groups of aquatic organisms included in these programs (Hellawell 1986). Aquatic macroinvertebrates include insects, aquatic worms, flatworms, leaches, shrimps, crabs, crayfish, clams and mussels among others. Aquatic macroinvertebrates are a widely accepted group for assessing the quality and functionality of streams and their ecosystems for a number of reasons (Weber 1973, Rosenberg and Resh 1993). First, most river and stream ecosystems have relatively diverse macroinvertebrate assemblages (100‐200 species in natural undisturbed temperate streams), with many species representing each of the major taxonomic orders (e.g., Ephemeroptera [mayflies], Trichoptera [caddisflies], Plecoptera [stoneflies], Coleoptera [beetles], Diptera [true flies] among others). Each species is to some degree unique; as a result, each potentially possesses different habitat and feeding preferences, tolerances to changes in environmental conditions, etc. Thus, together, the aquatic macroinvertebrates are a sensitive measure of current environmental conditions as well as a good measure of ecosystem change and stress over both space and time. Second, the relatively long life spans (a few months to a year or more) of macroinvertebrates make the presence or conspicuous absence of macroinvertebrate species at a site a meaningful record of environmental quality during the recent past. Third, their abundance lends itself to statistical analyses, which play an integral role in assessing the quality of habitat and water as well as ecosystem integrity. Fish provide additional information on water