Water Resources Professional Project Reports

Document Type

Technical Report

Publication Date

6-7-2013

Abstract

Mounting evidence suggests that a warming climate in the southwestern United States threatens the quality and quantity of mountain source waters for New Mexicos largest surface water source, the Rio Grande. These waters, fed primarily by snowmelt, are critical to the ecological, agricultural, municipal, and cultural requirements of New Mexico. In an effort to construct a baseline of stream metabolism in the East Fork of the Jemez River (EFJR), a major tributary of the Rio Grande, our research team sampled macrophytes, algae, macroinvertebrates, and benthic microbial communities to assess changes pertaining to habitat and seasonal fluctuations and in response to a devastating wildfire in the headwaters during the summer of 2011. This project focused specifically on the role of benthic heterotrophs in organic matter and nutrient cycling and export. Within the benthic microenvironments, retention, mineralization, assimilation, and recycling of particulate and dissolved organic matter occur. Particularly in autochthonous-dominated systems like the EFJR where algal-bacterial interaction controls organic matter processing, benthic microbes contribute significantly to ecosystem processes and are a key to understanding fluvial carbon and nutrient cycling. We conducted assays quantifying biofilm extracellular enzyme activity, the first step in microbial degradation of organic compounds, targeting prominent extracellular enzymes that change with the availability of carbon and nutrients in the sediments. Benthic sediments from three pools and three riffles on the EFJR were collected over a year's period to coincide with major seasonal events: the end of spring snowmelt, early summer, mid-summer, early fall after the monsoon season, and late fall. Water quality data on temperature, pH, dissolved oxygen, turbidity, specific conductivity, nitrate and soluble reactive phosphorus concentrations were collected using continuous monitoring equipment installed in the stream. Data on extracellular enzyme activities to specific substrates of organic carbon, nitrogen, and phosphorus were correlated with stream water quality parameters and nutrient data, macrophyte and algal biomass, and whole-stream metabolism to ascertain microbial response to habitat and seasonal fluctuations pertaining to metabolic processes and changes attributable to the summer wildfire. Results of the extracellular enzyme assays suggest that the EFJR is highly productive, generating high levels of activity of carbon (C)- and nitrogen (N)-acquisition enzymes correlating to high rates of gross primary productivity and community respiration. C- and N-acquisition ecoenzyme activities peaked in the month of greatest algal and macrophyte production (July) and were least active after spring snowmelt. Activities were generally higher in pools than in riffles, correlated with the greater biomass of macrophytes and algae in the pools. Stoichiometric ratios of the ecoenzyme activities were calculated and C:N, C:P, and N:P ratios were consistent throughout the year with little seasonal fluctuation, suggesting autotroph-heterotroph interactions are in dynamic equilibrium. Post-fire effects were pronounced, with drops in C- and N-acquisition enzyme activities and spikes in phosphorus (P)-acquisition ecoenzyme activities, up nearly 9 X pre-fire levels. Instream nutrients, specific conductivity, and turbidity increases, dissolved oxygen sags, and a 70% drop in macrophyte biomass at our site was attributed to major physical disturbances from unusually high overland flow upstream in the burned headwater forests. Increased nutrients mobilized from meadow soils and leached from the phosphate-rich ash load may have triggered the dramatic phosphatase response. Extracellular enzyme activity may prove to be an important metric for understanding the complex processes of organic matter cycling in aquatic ecosystems. Coupled with traditional parameters of water quality as monitoring tools, ecoenzyme assays may provide evidence of ecosystem changes due to climactic and anthropogenic alterations in watersheds critical to the water supply of New Mexico.

Language (ISO)

English

Keywords

Bioproductivity--New Mexico--Jemez River, East Fork., Heterotrophic bacteria--Climatic factors--New Mexico--Jemez River, East Fork., Microbial enzymes--New Mexico--Jemez River, East Fork., Stream ecology--New Mexico--Jemez River, East Fork., Freshwater ecology--New Mexico--Jemez River, East Fork., Ecophysiology--New Mexico--Jemez River, East Fork.

Comments

A Professional Project Report submitted in partial fulfillment of the requirements for the degree of Master of Water Resources, Water Resources Program, University of New Mexico.

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