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Research Project: Strategic Investigations to Improve Water Quality and Ecosystem Sustainability in Agricultural Landscapes

Location: Water Quality and Ecology Research

Title: Spatial, temporal, and experimental: three study-design cornerstones for establishing defensible numeric criteria for freshwater ecosystems

item Taylor, Jason
item BACK, JEFFREY - Baylor University
item BROOKS, BRYAN - Baylor University
item KING, RYAN - Baylor University

Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2018
Publication Date: 4/18/2018
Citation: Taylor, J.M., Back, J.A., Brooks, B.W., King, R.S. 2018. Spatial, temporal, and experimental: three study-design cornerstones for establishing defensible numeric criteria for freshwater ecosystems. Journal of Applied Ecology.

Interpretive Summary: Excess nutrients from wastewater and agricultural runoff globally threaten freshwater and marine ecosystems. Despite widespread recognition of the negative impacts of phosphorus enrichment on water resources critical to natural ecosystems and human society, development of criteria to prevent degradation of water bodies is moving at a slow pace. An ARS research ecologist and his university collaborators demonstrate that a multi-faceted approach, relying on repeated sampling to capture variability on annual and seasonal timescales combined with experimental mesocosm data, can identify consistent and therefore robust ecological responses to nutrient enrichment that may serve as early indicators of low level enrichment. Our approach can be used by resource managers to reduce impacts of nutrient pollution to the nation's water resources.

Technical Abstract: Robust stressor-response measures are needed to inform nutrient criteria development and protect inland waters from impacts associated with eutrophication. We tested a framework to help inform criteria development that relies on assessing stream assemblage responses to phosphorus (P) enrichment across multiple years, seasons, and under controlled experimental conditions using diatom species composition. Diatom species composition was strongly correlated to total phosphorus (TP) across a network of 26 field sites during summer months of two hydrologically distinct years, despite shifts in species composition associated with changes in algal biomass. Species composition at 6 intensive sites revealed that diatom assemblages responded consistently according to the P gradient, despite weak evidence for and interaction with changing biomass associated with variable stream conditions over 8 seasons. Species composition on rocks originating in a low P stream and exposed to moderate and high P conditions in mesocosms were similar and consistent with assemblages at P enriched field sites, whereas rocks transplanted to control mesocosms had significantly different assemblages resembling reference field sites. Threshold Indicator Taxa Analysis identified synchronous declines in several alga species that resulted in assemblage thresholds associated with TP concentrations > 20 and 25 µg L-1 for 2006 and 2007 respectively. The consistent ecological responses to P enrichment observed across multiple sampling events and in our stream mesocosm experiment validates a simple framework that can be transferred to other regions to inform nutrient criteria development and prevent stream ecosystems from shifting toward eutrophic conditions that increasingly threaten global water resources.