Principal Investigator: Judith Meyer (University of Georgia)
Sponsor: GWRI
Start Date: 2001-03-01; Completion Date: 2002-02-28;
Keywords: Ecosystem processes, Basin-wide analysis for water management, Solute transport, Flow regime, Apalachicola-Chattahoochee-Flint River Basin
Problem and Research Objectives:
The quantity and timing of river flow is critical to the ecological integrity of river systems (Poff et al.1997). Flow is strongly correlated with physical and chemical characteristics of the river such as channel shape, water temperature and velocity,and habitat type and complexity (Jowett and Duncan 1990,Poff et al.1997). Five main components of the flow regime impact ecological processes:magnitude of discharge at critical time periods,frequency of the various discharge magnitudes,duration of time associated with a particular discharge,timing or predictability of discharge events of particular magnitudes,and the rate of change of hydrologic conditions (Richter et al. 1996,Poff et al.1997) .These five components of the flow regime influence the ecological dynamics of river systems directly and indirectly by affecting water quality, energy sources,physical habitat,and biotic interactions (Karr 1991,Poff et al.1997).
Although there are many different types of hydrologic and channel alterations that result in changes to the flow regime,dams are one of the most conspicuous and prevalent forms of flow alteration on large and some smaller rivers and streams.In the contiguous United States,there are only 42 rivers with greater than 200 river kilometers unregulated by major dams (Benke 1990).Though there have been a number of studies of the impacts of dams on channel morphology (Ligon et al.1995),fish (Moyle et al.1998), habitat availability (Bogan 1993),and riparian species survival and recruitment (Rood et al.1995),less is known about the impact of dams and flow regime on basic ecosystem processes such as nutrient uptake and metabolism,especially in larger rivers.In many cases,these ecosystem processes are directly linked to the ecosystem services (e.g.water supply,pollution control, and fisheries)expected from the river system.
We are studying the relationship between flow and nutrient uptake and metabolism on the Chattahoochee River below Atlanta.The fixation of energy through primary production and the subsequent release through respiration are primary ecosystem functions,and the addition or loss of energy to the system can influence energy flows in downstream systems.In order to determine net addition or loss of energy to the system, net daily metabolism can be calculated.Net daily metabolism is defined as the difference between gross primary productivity and total system respiration (Bott 1996). Metabolism has been shown to vary with high stream discharge as a result of shifts in primary production (Uehlinger and Naegeli 1998).However,relationships between net daily metabolism and low flow conditions are uncertain,particularly in large river systems.
The uptake and processing of nutrients by rivers is essential to maintaining downstream and instream water quality.In unregulated rivers,the downstream ecosystems that could be affected by high nutrient loadings are typically estuaries. However,in regulated rivers,there are typically a series of reservoirs that are connected by sections of flowing water.This is the situation on the Chattahoochee River.In addition,the flowing river section between Lake Lanier and West Point Lake receives approximately 220 million gallons a day of wastewater treatment plant effluent (Frick et al.1996).The retention and transformation of the nutrients associated with these inputs is essential to maintaining water quality in this section of the river and in West Point Lake.Nutrient uptake length is the length of stream traveled by the average nutrient molecule in the water column before being taken up by biota (Stream Solute Workshop 1990).Nutrient uptake lengths in small streams is related to discharge (Stream Solute Workshop 1990).Uptake lengths in streams receiving wastewater treatment plant effluent are typically much longer than uptake lengths in streams with similar discharge but no wastewater inputs (Marti et al.In press).However,it is uncertain how nutrient uptake lengths vary with low flows in large rivers.
Our objectives were to determine how net ecosystem metabolism and nutrient uptake lengths vary with discharge under baseflow conditions in the Chattahoochee River below Atlanta.In addition,we wanted to determine the importance other factors that may influence metabolism and nutrient uptake such as temperature,total suspended solids,light,dissolved organic carbon,water column chlorophyll a concentrations,and nutrient concentrations.We hope that these analyses will help to give a better understanding of how flow regime influences ecosystem processes in a regulated river.