Two Decades of Variability in Nutrient Budgets for Ice-Covered, Closed Basin Lakes in the McMurdo Dry Valleys, Antarctica
Abstract
The McMurdo Dry Valleys (MCM) of Antarctica represent one of the world's driest deserts. A collection of permanently ice-covered lakes in the MCM provide an important refuge for microorganisms. Thus, it is of interest to understand the nutrient dynamics of these lakes and how these dynamics have changed over time. One to two decade-long records of physical, chemical, and biological characteristics in the East Lobe of Lake Bonney (ELB), Lake Fryxell (FRX), and Lake Hoare (HOR) allowed for development of annual nutrient budgets and analysis of possible causes of variability. Annual nutrient budgets were built by accounting for total seasonal streamflow and average seasonal nutrient concentration in streamflow, as well as nutrient diffusion across the chemocline, which roughly coincides with the bottom of the photic zone. Unaccounted-for changes in nutrient content were assumed to be caused by processes internal to the lake. Changes to the proportion of lake volume in the photic zone, seasonal streamflow, and biological activity, represented by chlorophyll-a (CHL) concentration, were considered as potential explanations. For all three lakes, nutrient diffusion either into or out of the photic zone was minimal compared to nutrient inputs from streamflow. The sole exception to this was NH4 inputs to FRX; for eight of the nine years considered, diffusive inputs of NH4 to the photic zone were greater than streamflow inputs. In most cases, internal processes appeared to dominate over streamflow inputs; this is likely because seasonal streamflow represented less than 8% of the photic zone volume in all three lakes. Three exceptions to this trend were the phosphorus budget in ELB, and the NH4 and NO3 budgets in HOR; in these cases, streamflow inputs represented a notable portion of the annual nutrient budgets. The MCM lakes decreased in volume from the early 1990s to the early 2000s; they have since been increasing in volume. The volume of the photic zone was positively correlated to the mean concentrations of NH4 and NO3 in ELB, and to the mean NO2 concentration in FRX. Mean CHL concentration in the photic zone was positively correlated to mean NO2 concentration in ELB; mean CHL concentration in the photic zone was negatively correlated to mean NO2 concentration in HOR. These results suggest that internal nutrient cycling processes dominate the nutrient dynamics of the MCM lakes. To further explore inputs from biological processes, the potential for diffusion from benthic microbial mats in shallow waters could be considered.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMGC53B1057T
- Keywords:
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- 0746 CRYOSPHERE Lakes;
- 0470 BIOGEOSCIENCES Nutrients and nutrient cycling;
- 1615 GLOBAL CHANGE Biogeochemical cycles;
- processes;
- and modeling;
- 1621 GLOBAL CHANGE Cryospheric change