Hydrological Controls on Ecosystem Dynamics in Lake Fryxell, Antarctica

Abstract

The McMurdo Dry Valleys constitute the largest ice free area of Antarctica. The area is a polar desert with an annual precipitation of ∼ 3 cm water equivalent, but contains several lakes fed by glacial melt water streams that flow from four to twelve weeks of the year. Over the past ∼20 years, data have been collected on the lakes located in Taylor Valley, Antarctica as part of the McMurdo Dry Valley Long-Term Ecological Research program (MCM-LTER). This work aims to understand the impact of climate variations on the biological processes in all the ecosystem types within Taylor Valley, including the lakes. These lakes are stratified, closed-basin systems and are perennially covered with ice. Each lake contains a variety of planktonic and benthic algae that require nutrients for photosynthesis and growth. The work presented here focuses on Lake Fryxell, one of the three main lakes of Taylor Valley; it is fed by thirteen melt-water streams. We use a functional regression approach to link the physical, chemical, and biological processes within the stream-lake system to evaluate the input of water and nutrients on the biological processes in the lakes. The technique has been shown previously to provide important insights into these Antarctic lacustrine systems where data acquisition is not temporally coherent. We use data on primary production (PPR) and chlorophyll-A (CHL)from Lake Fryxell as well as discharge observations from two streams flowing into the lake. Our findings show an association between both PPR, CHL and stream input.

Fig 1. Aerial view of Taylor Valley, Antarctica and a schematic representation of Canada, Lost Seal and Von Guerard streams.

Image available at http://earthobservatory.nasa.gov/IOTD/view.php?id=35535.

Fig 2. Boxplots for the observed primary production (PPR (μgC/(L × day)), top) and Chlorophyll A (CHL,(μg(Chlorophyll − A)/L) lower) values for the 1995–2011 period.

The black line connects the average values for each season, marked with a black dot.

Fig 3. Log-Daily average discharge rates (black dots) for the Canada stream (top panels), Lost Seal stream (middle panels) and Von Guerard (lower panels) for the 1996–1997, 2005–2006 and 2009–2010 seasons.

On each panel, we overlay the corresponding average daily temperature.

Fig 4. Time series of the daily averages of the air temperature at Lake Fryxell during the 1993–2010 period.

For each year, we consider the months of December and January, which are used in our analysis.

Fig 5. A schematic representation of the functional regression approach described in Section.

Fig 6. Observed log-discharge rates (dots) for the Canada stream (top panels), Lost Seal stream (middle panels) and Von Guerard stream (lower panels), for the 1996–1997, 2003–2004, 2007–2008 and 2010–2011 seasons.

The green curves represent the predicted log-discharge for the four selected seasons. The horizontal blue line is at log(0.01) which represents zero discharge.

Fig 7. Observed (dots) and fitted (stars) PPR (top panel) and CHL (lower panel) values for the 1995–2011 period.

The vertical dashed lines represent predicted value ± 2 × standard errors for each season.