Cathy M. Tate

Inorganic N and P dynamics of Antarctic glacial meltwater streams as controlled by hyporheic exchange and benthic autotrophic communities

Abstract The McMurdo Dry Valleys of South Victoria Land, Antarctica, contain numerous glacial meltwater streams that drain into lakes on the valley floors. Many of the streams have abundant perennial mats of filamentous cyanobacteria. The algal mats grow during streamflow in the austral summer and are in a dormant freeze-dried state during the rest of the year. NO3 and soluble reactive P (SRP) concentrations were lower in streams with abundant algal mats than in streams with sparse algal mats. NO3 and SRP concentrations were higher in the hyporheic zone of a stream with abundant algal mats than in the stream itself. An experimental injection of LiCl, NaNO3, and K3PO4 was conducted in Green Creek, which has abundant algal mats. Substantial hyporheic exchange occurred. The NO3 and PO4 concentrations at 50 m below the injection were 55 μM and 18 μM, respectively, during the experiment. NO3 and PO4 concentrations were below the detection limit of 1 to 2 μM at a site 497 m below the injection during the Cl tracer arrival, indicating a high capacity for nutrient uptake by algal communities. NO2 and NH4 were present at sites 226 and 327 m below the injection, indicating that, in addition to denitrification and algal uptake, dissimilatory NO3 reduction to NO2 and NH4 may be a NO3 sink during transport. Transport modelling with nutrient uptake represented as a 1st-order process yielded reach-scale parameters of 4.3 × 10−5 to 3.9 × 10−4/s and 1.4 × 10−4 to 3.8 × 10−4/s for uptake of NO3 and PO4, respectively. The best match with the observed data was a model in which PO4 uptake occurred only in the main channel and NO3 uptake occurred in the main channel and in the hyporheic zone. Hyporheic NO3 uptake was 7 to 16% of the total uptake for the different stream reaches. These results demonstrate that nutrient flux to the lakes is controlled by hyporheic exchange and nutrient uptake by algal mats in dry valley streams. Streams without algal mats contribute more nutrients to the lakes than streams with algal mats.

Methane consumption and carbon dioxide emission in tallgrass prairie: Effects of biomass burning and conversion to agriculture

Consumption of atmospheric methane and emission of carbon dioxide by soils were measured on unburned and annually burned tallgrass prairie and on adjacent wheat and sorghum agricultural plots in Kansas. Profiles of CH4 and CO2 concentration with soil depth were also measured. Overall patterns of CH4 consumption by soils varied temporally, with soil depth and land use. Mean CH4 consumption for the 200-day sampling period was −1.02 mg CH4 m−2 d−1 (SE=0.13, n=41) for burned prairie, −0.63 (SE=0.09, n=45) for unburned prairie, −0.85 (SE=0.20, n=36) for wheat, and −0.45 (SE=0.08, n=40) for sorghum. Less than 20 % of the variance in CH4 consumption was explained by soil temperature and/or moisture content. Overall patterns of CO2 emission from prairie and agricultural soils varied temporally, but not among land use. Mean CO2 emission for the 200-day sampling period was 15.7 g CO2 m−2 d−1 (SE=1.8, n=41) for burned prairie, 14.5 (SE=1.3, n=45) for unburned prairie, 13.9 (SE=2.1, n=36) for wheat, and 10.3 (SE=2.1, n=40) for sorghum. More than 70% of the variance in prairie CO2 emission rate was explained by soil temperature and moisture. Crop management practices influenced the timing of CO2 emission from agricultural plots but not the net annual rate of emission. Methane concentrations generally decreased and CO2 concentrations increased with soil depth, and the magnitude of CH4 and CO2 flux generally increased with increased magnitude of the soil gas concentration gradient. Fertilization of agricultural fields had no measured effect on CH4 or CO2 flux or on soil gas concentrations.

Modeling biotic habitat high risk areas

Summary Fire, especially stand replacing fire, poses a threat to many threatened and endangered species as well as their habitat. On the other hand, fire is important in maintaining a variety of successional stages that can be important for other animals such as elk. Methods are given here on a variety of ways to approach risk assessment to assist in prioritizing areas for allocation of fire mitigation funds. One example looks at assessing risk to the species and biotic communities of concern followed by the Colorado Natural Heritage Program. One looks at the risk to Mexican spotted owls. Another looks at the risk to cutthroat trout, and a fourth considers the general effects of fire and elk.