Paleolimnology in Roosevelt: Learning from the Past
Proposal Submitted to State of Arizona Water, Economic Development and Sustainability Fund • Principal Investigators: – Owen K. Davis, UA – Susan Fitch, ADEQ – Paul Gremillion, NAU – Vicente Lopes, UA – Peter Van Metre, USGS – David Walker, UA
Problem Statement • In waters without historical water quality data, it is difficult to predict trends in trophic state. • It is impossible to quantify detrimental effects of land-use activities or natural disturbances unless data has been collected prior to each disturbance or activity.
Paleolimnology as a Tool • Paleolimnological techniques are often used to assess water quality trends in lakes over time. • Incorporated in reservoir sediments is a record of the organisms that lived in and around the lake, as well as proxy data related to processes occurring in the lake.
• Previous studies have examined the accumulation of watershed-derived pollutants in sediment cores of reservoirs with rapidly urbanizing watersheds. • These studies often fail to address the consequences of these pollutants on aquatic biota or overall ecosystem processes.
Specifically we propose to; • We propose to use paleolimnological techniques to obtain, date, and analyze sediment cores from Roosevelt. • These cores will then be age dated using Pb 210 and/or Cs 137 radionuclides.
Objectives • To quantify long-term water quality trends in Roosevelt and the Salt River watershed • Determine how these watershed determinants define water quality within the reservoir • How aquatic biota have responded to these water quality changes
Objectives (cont.) • Determine watershed vegetation changes over time and how this has affected, and been affected by, fire cycle frequency and intensity. • Determine the effect of anthropogenic activities in the watershed on water quality in the reservoir.
• The focus of this work will be pre- impoundment, however, local geography indicates a pre- impoundment playa or wetland may have existed (i.e., “Tonto Basin ”). • We anticipate the cores being long enough to capture pre-impoundment conditions.
Analytes and the reason for their analysis. • Fossilized pollen grains (palynology) – To determine watershed vegetative changes which will vary due to climate, wildfire regimen, or human removal. – Decreases in vegetation can reduce transpiration and soil moisture storage which may increase runoff and material transported to the reservoir. – The rate of this transport, in turn, can strongly influence biogeochemical processes within the reservoir.
• Fossilized diatom frustules – Siliceous diatom valves are well-preserved in lake sediments and are a direct reflection of environmental conditions at the time of deposition. – Diatoms contain many species with relatively limited ecological tolerances. – Short life cycles mean they respond rapidly to environmental change. – Have been used to infer changes in pH, salinity, temperature, and nutrient availability.
• Fossilized chironomid (midge fly) head capsules – Excellent indicators of water quality condition especially of hypolimnetic anoxia. – Chironomids highly sclerotized head capsules are usually well-preserved in sediments. – Chironomid taxa exhibit marked differences in individual responses to water quality degradation leading to anoxia such as nutrient accumulation.
• Charcoal Analysis – To determine past fire cycle, frequency, and intensity. – The consequences of fire on Roosevelt water chemistry is a timely and important issue considering current drought conditions.
• Nutrients and heavy metals – We will obtain samples at select locations of the core for nutrients related to eutrophication and metals associated with wither anthropogenic activities or atmospheric input.
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