Research Projects

Project at a Glance

Project Status: complete

Title: Long-term studies of lakes and watersheds in the Sierra Nevada, patterns and processes of surface water acidification

Principal Investigator / Author(s): Melack, John M

Contractor: Marine Science Institute, UC Santa Barbara

Contract Number: A932-060


Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition


Abstract:

The atmospheric deposition hydrology, hydrochemistry and zooplankton of seven high altitude Sierran catchments have been studied for two years (1989-l99l) to assess potential effects of acidic deposition. Atmospheric deposition of water and solutes was determined by event collections of rain and by snow sampling at the time of maximum accumulation. Year-round bimonthly samples for solutes and zooplankton were obtained from each lake. Lake outflows were sampled bimonthly except during snowmelt when collections were made every one to two weeks. Continuous records of outflow discharge were obtained. All major solutes in atmospheric deposition (H, NH4, Ca, Mg, Na. K. N03, S04. Cl. formate and acetate) and lake and stream water (H. ~'H4. Ca. Mg. Na. K. N03. S04. Cl. acid neutralizing capacity [ANC] and silica) were measured. A rigorous quality assurance-quality control protocol was followed. Sierra snow is slightly acidic (seasonal average among sites. pH 5.2 to 5.4), and rain is usually more acidic (seasonal average among sites. pH 4.6 to 5.5). Volume-weighted mean annual pH ranged from 5.1 to 5.4 among the seven catchments. The acidity is caused by weak organic acids and strong acids of nitrate and sulfate. All seven catchments retain annually the atmospheric input of H and export ANC and similar amounts of basic cations. Hence. the weathering and exchange processes in the catchments are sufficient to buffer current acidic atmospheric deposition on an annual basis. During snowmelt pH and ANC minima occur each year. Zooplankton species known to be intolerant of acidification occur in all seven lakes. and their presence is evidence that Sierran lakes are not currently showing chronic biological effects of acidic deposition.


 

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