46 research outputs found
RATES, IMPORTANCE, AND CONTROLS OF NITROGEN FIXATION IN OLIGOTROPHIC ARCTIC LAKES, TOOLIK, ALASKA
No full textBiological nitrogen (N) fixation of atmospheric N2 by free-living cyanobacteria in aquatic environments is common, and in many ecosystems, it can account for a significant portion of the biologically available N inputs. Although N fixation can compensate for N limitation, N limitation is maintained over relatively long time scales in many oligotrophic lake ecosystems. This dissertation examines the importance of benthic and pelagic N fixation in the N economies of oligotrophic lakes in arctic Alaska (Chapter 1) and examines nutrient, light, and grazer controls on benthic N fixation (Chapters 2 and 3). Both benthic and pelagic N fixation are prevalent in many lakes across the Alaskan arctic landscape, ranging from 0.12 ? 1.5 mg N m-2 day-1 and 0 ? 2.56 mg N m-2 day-1 respectively. Pelagic N fixation is much higher than has been reported elsewhere for oligotrophic lakes, and is more important than previously thought, comprising ~ 75% of N inputs to one lake. Benthic N fixation is lower than has been reported for other oligotrophic systems, and is roughly equivalent to N inputs from atmospheric deposition on an areal basis (~25 mg N m-2 year-1). On the landscape scale, N fixation in lakes roughly equal that in terrestrial ecosystems in this Arctic region. Benthic N fixation generally appears to have a saturating response to light availability within individual lakes, but light does not explain variation in benthic N fixation across lakes or years. Whole-lake fertilization and laboratory experiments indicate that P input stimulates benthic N fixation while N input suppresses N fixation when N is added either alone or in conjunction with P in Redfield proportion. Snails at ambient density cause a small decline in benthic N fixation (0.85 ? 1.8% reduction over the summer). These patterns are corroborated in the landscape: lakes on younger surfaces have higher P, more snails, and higher rates of N-fixation than lakes on older surfaces
Water quality and greenhouse gas (GHG) concentration data for temperate headwater streams in Germany
No full textThe dataset contains yearlong monthly measurements (June 2020 to April 2022) of water quality parameters, CO2, CH4 and N2O concentrations from 23 streams, 3 drainage ditches and 2 wastewater effluent sites within within the Loisach, Schwingbach and Neckar catchments in Germany. The study sites covered various upstream land uses (croplands, wetlands, grasslands, settlements and forests) as well as stream orders (1-6). Measurements were mostly done during the day between 8.00 am and 5.00pm
Water quality and greenhouse gas (GHG) concentration data from streams and rivers in the tropical Mara basin
No full textThe dataset contains yearlong monthly measurements (January 2019 to Febuary 2020) of water quality parameters, CO2, CH4 and N2O concentrations from 59 stream sites within the Kenyan part of the Mara River basin. The study sites covered various upstream land uses (croplands, savanah grasslands and forests) as well as stream orders (1-8). Measurements were mostly done during the day between 8.00 am and 5.00pm
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A comparison of whole and thin-sectioned otolith aging techniques and validation of annuli for Arctic grayling
No full textInformation on age and growth is essential for the conservation and management of fish species. Age is often estimated using the banding structure in otoliths, but the technique used can influence the estimate, especially in slow-growing, long-lived species. Counts of translucent bands from both whole and thin-sectioned Arctic grayling (Thymallus arcticus) otoliths from the Kuparuk River, Alaska, gave similar age estimates. Age estimates from whole otoliths were less variable, particularly for older age groups, and were much easier to prepare and read than thin-sections. Comparison of growth of individual tagged fish to a von Bertalanffy growth model revealed that the translucent rings are true annuli. This approach to validation may be most useful in northern latitudes where other techniques are impractical. Our study shows that whole otoliths provide a fast, reliable, cost-effective technique for age estimation of this long-lived, slow-growing fish species common to the North American Arcti
Controls of Benthic Nitrogen Fixation and Primary Production from Nutrient Enrichment of Oligotrophic, Arctic Lakes
No full text© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecosystems 16 (2013): 1550-1564, doi:10.1007/s10021-013-9701-0.We examined controls of benthic dinitrogen (N2) fixation and primary production in oligotrophic lakes in Arctic Alaska, Toolik Field Station (Arctic Long-Term Ecological Research Site). Primary production in many oligotrophic lakes is limited by nitrogen (N), and benthic processes are important for whole-lake function. Oligotrophic lakes are increasingly susceptible to low-level, non-point source nutrient inputs, yet the effects on benthic processes are not well understood. This study examines the results from a whole-lake fertilization experiment in which N and P were added at a relatively low level (4 times natural loading) in Redfield ratio to a shallow (3 m) and a deep (20 m) oligotrophic lake. The two lakes showed similar responses to fertilization: benthic primary production and respiration (each 50–150 mg C m−2 day−1) remained the same, and benthic N2 fixation declined by a factor of three- to fourfold by the second year of treatment (from ~0.35 to 0.1 mg N m−2 day−1). This showed that the response of benthic N2 fixation was de-coupled from the nutrient limitation status of benthic primary producers and raised questions about the mechanisms, which were examined in separate laboratory experiments. Bioassay experiments in intact cores also showed no response of benthic primary production to added N and P, but contrasted with the whole-lake experiment in that N2 fixation did not respond to added N, either alone or in conjunction with P. This inconsistency was likely a result of nitrogenase activity of existing N2 fixers during the relative short duration (9 days) of the bioassay experiment. N2 fixation showed a positive saturating response when light was increased in the laboratory, but was not statistically related to ambient light level in the field, leading us to conclude that light limitation of the benthos from increasing water-column production was not important. Thus, increased N availability in the sediments through direct uptake likely caused a reduction in N2 fixation. These results show the capacity of the benthos in oligotrophic systems to buffer the whole-system response to nutrient addition by the apparent ability for significant nutrient uptake and the rapid decline in N2 fixation in response to added nutrients. Reduced benthic N2 fixation may be an early indicator of a eutrophication response of lakes which precedes the transition from benthic to water-column-dominated systems.This project was supported by
NSF-OPP 9732281, NSF-DEB 9810222, NSF-DEB
0423385, and by a Doctoral Dissertation Improvement
Grant NSF-DEB 0206173. Additional funding
was provided by the Small Grants Program through
the NSF-IGERT Program in Biogeochemistry and
Environmental Change at Cornell University
A comparison of whole and thin-sectioned otolith aging techniques and validation of annuli for Arctic grayling
No full textInformation on age and growth is essential for the conservation and management of fish species. Age is often estimated using the banding structure in otoliths, but the technique used can influence the estimate, especially in slow-growing, long-lived species. Counts of translucent bands from both whole and thin-sectioned Arctic grayling (Thymallus arcticus) otoliths from the Kuparuk River, Alaska, gave similar age estimates. Age estimates from whole otoliths were less variable, particularly for older age groups, and were much easier to prepare and read than thin-sections. Comparison of growth of individual tagged fish to a von Bertalanffy growth model revealed that the translucent rings are true annuli. This approach to validation may be most useful in northern latitudes where other techniques are impractical. Our study shows that whole otoliths provide a fast, reliable, cost-effective technique for age estimation of this long-lived, slow-growing fish species common to the North American ArcticGettel et al "A comparison of whole and thin-sectioned otolith aging techniques and validation of annuli for Arctic grayling." Northwest Science. 1997; 71(3): 224-23
The effects of grazing by the snail, Lymnaea elodes, on benthic N2 fixation and primary production in oligotrophic, arctic lakes
No full textClassification of Geomorphic Units and Their Relevance for Nutrient Retention or Export of a Large Lowland Padma River, Bangladesh: A NDVI Based Approach
No full textGeomorphic classification of large rivers identifies morphological patterns, as a foundation for estimating biogeochemical and ecological processes. In order to support the modelling of in-channel nutrient retention or export, the classification of geomorphic units (GUs) was done in the Padma River, Bangladesh, a large and geomorphically-complex lowland river. GUs were classified using the normalized difference vegetation index (NDVI) four times over a year, so as to cover the seasonal variation of water flows. GUs were categorized as primary and secondary channels (C & S); longitudinal bar (L); transverse bar (T); side bar (SB); unvegetated bank (EK); dry channel (ED); island (VI); and water depression (WD). All types of GUs were observed over the four distinct annual seasons, except ED, which was absent during the high flow, monsoon season. Seasonal variation of the surface area of GUs and discharge showed an inverse relation between discharge and exposed surface areas of VI, L, T, and SB. Nutrients mainly enter the river system through water and sediments, and during monsoon, the maximum portion of emergent GUs were submerged. Based on the assumption that nutrient retention is enhanced in the seasonally inundated portions of GUs, nutrient retention-/export-relevant geomorphic units (NREGUs) were identified. Seasonal variation in the area of NREGUs was similar to that of GUs. The mean NDVI values of the main identified NREGUs were different. The variation of NDVI values among seasons in these NREGUs resulted from changes of vegetation cover and type. The variation also occurred due to alteration of the surface area of GUs in different seasons. The changes of vegetation cover indicated by NDVI values across seasons are likely important drivers for biogeochemical and ecological processes.Water Resource
