Coupling Concentration‐ and Process‐Discharge Relationships Integrates Water Chemistry and Metabolism in Streams. Issue 12 (6th December 2019)

• Record Type: Journal Article
• Authors: O'Donnell, B.; Hotchkiss, E. R.
• Is Part Of: Water resources research. Volume 55:Issue 12(2019)
• Page Start: 10179
• Page End: 10190
• Publication Date: 2019-12-06
• Subjects: concentration‐discharge -- metabolism -- catchment, C‐Q; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2019WR025025
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Stream ecosystem processes, such as metabolism, are dynamically impacted by flow intensity. Therefore, without integrating ecosystem processes with water quality, we miss opportunities to develop frameworks to understand metabolic responses to changing flow. Flow simultaneously affects the material transport and biological opportunities for material transformation. Combining the strengths of ecohydrology and stream ecology to understand how flow variation alters ecosystem processes, we analyzed more than 5 years of water quality and stream metabolism data. We created segmented process‐discharge (P‐Q) relationships to examine how metabolism rates vary across discharge and compared them to concentration‐discharge (C‐Q) relationships to explore the dynamic effects of discharge on processes and physicochemical parameters. Within the segmented P‐Q relationships, we found the behavior of ecosystem respiration (ER), gross primary production (GPP), and net ecosystem production (NEP) to be different at high and low flows with varying degrees of statistical significance, demonstrating the potential for divergent metabolic responses across changing flows. GPP declined with increasing discharge. The rate of ER declined with discharge initially but then became unchanging at higher flows. NEP reflected the divergent trends between ER and GPP, as the relationship of NEP to Q was flat at lower discharge and declined at higher flows. Interrelated physicochemical parameters and ecosystem processes, such as pH and NEP, had mirrored responses to discharge. Coupling analyses of flow, water quality, and metabolism offers a more complete picture of interrelated ecosystem processes, allowing for a better understanding of ecosystem response to the physical and chemical changes that occur across flows. Plain Language Summary: Understanding how stream microorganisms respond to changes in water flow is needed to improve the health of aquatic ecosystems. While high discharge is frequent when nutrients and pollutants are swept downstream, we lack information about how biology and water quality change during high flow. To examine water quality across flows, concentration‐discharge relationships are often quantified. However, by only looking at how water quality changes as a function of flow, we miss a key piece of information: Life within the stream. Life within a stream influences and is influenced by water quality and flow. Here, we used 5 years of chemistry and flow data to calculate stream metabolism: The processes of photosynthesis and respiration by the life within a stream. To assess how water quality changes across flow, we (1) identified how stream metabolism changes across flow via process‐discharge analyses and (2) compared concentration‐discharge and process‐discharge trends to discover how they influenced one another. We found that stream metabolism exhibited different responses across flows. Moreover, multiple concentration‐discharge relationships had mirrored responses to associated process‐discharge relationships. This study ultimately reveals that both transport and biology respond to changes in flow, with the potential to regulate key ecosystem behaviors. Key Points: We propose a novel way to integrate biotic processes with concentration‐discharge trends via process‐discharge relationships Low and high flows induce distinct trends in gross primary production, ecosystem respiration, and net ecosystem production Interrelated physicochemical parameters and ecosystem processes, such as pH and net ecosystem production, follow mirrored trends