Alan W. Groeger

FACTORS CONTROLLING PRIMARY PRODUCTION IN LAKES AND RESERVOIRS: A PERSPECTIVE

ABSTRACT Phytoplankton productivity and biomass fluctuations are controlled by the same energy and nutrient inputs and the same balance of gain and loss factors in natural and manmade lakes. However, some significant physical and hydrodynamic differences between lakes and reservoirs do exist which influence (1) the relative contributions of various primary producers to their food-webs, (2) the relative importance of certain limiting factors to primary production (e.g., turbidity, nutrient availability, flushing rate), (3) the spatial variability of primary production within reservoirs, and (4) the applicability of lake-based classifications and empirical relationships to reservoirs. An important distinction between most natural and manmade lakes is that reservoirs are semi-fluvial environments that fall between rivers and lakes on a continuum of aquatic ecosystems. A wider recognition of the riverine influences on reservoir ecosystems will enhance our understanding of the spatial and temporal heterogeneit...

Chemical Classification and Trophic Characteristics of Texas Reservoirs

ABSTRACT Texas reservoirs were classified into three groups by cluster analysis based upon the following properties of their surface waters: specific conductance, alkalinity, calcium, sulfate, pH, chloride, and sodium (listed in descending order of importance as discriminators). The three groups of reservoirs had a distinct geographic distribution corresponding to a strong east-west gradient of increasing aridity and differences in surface geology. Chemical characteristics of the western reservoirs were most influenced by the dissolution of evaporites formed in the geological past and current arid conditions (median specific conductance = 1817 μS cm−1; median alkalinity = 120 mg CaCO3 L−1). Sulfate and chloride accounted for 87% of the major anions (in equivalent charge concentrations). The second group of reservoirs, located in a wide band through central Texas, were dominated by weathering of limestone bedrock and calcareous soils (median specific conductance = 518 μS cm−1; median alkalinity = 133 mg Ca...

Metabolism of 2-chlorobiphenyl by suspension cultures of Paul's Scarlet rose

Several studies have shown that plant-soil systems were capable of degrading chlorinated biphenyls, with the resulting accumulation of breakdown products in both the plants and the soil. However, since these studies were performed under field conditions, it is not certain what portion of the degradation was due to plant metabolism and what portion to that of soil microbes which have been demonstrated in pure culture to degrade chlorinated biphenyls. This question is addressed in the present research by determining the metabolism of (/sup 14/C)-labeled 2-chlorobiphenyl provided aseptically to axenic cultures of Pauls Scarlet rose.

Polychlorobiphenyl (PCB) metabolism by plant cells

SummarySuspension cultures of Pauls Scarlet rose provided with 0.3 ppm of 2,2′, 4,4′-tetrachlorobiphenyl metabolized the compound at a rate of 45 proles· n−1·g dry wt−1. The environmental and technological significance of plants to metabolize environmentally persistent compounds is discussed.

Nutrient limitation in Crater Lake, Oregon

Experiments were carried out to determine what nutrient (or nutrients) was primarily responsible for limiting phytoplankton productivity in ultraoligotrophic Crater Lake. The experiments included in situ and laboratory nutrient addition bioassays utilizing the natural phytoplankton community, Selenastrum capricornutum bottle assays, photosynthetic responses, photosynthetic carbon metabolism, and response of dark uptake of 14CO2 with the addition of NH 4 + . The results suggested that a trace metal(s) or its availability was the primary factor limiting the epilimnetic phytoplankton productivity. Nitrogen was extremely low, and quickly became limiting with the addition of trace metals and a chelator. Iron is the most likely candidate as the limiting nutrient. Trace metals and nitrogen are also both important in limiting phytoplankton at 100 m, a depth where biologically mediated turnover of nutrients seems to be more important.

Relationship between photosynthetic and respiratory carbon metabolism in freshwater phytoplankton

Measurements of algal carbon metabolism in the light and the dark were conducted in (1) short-term (3-h) light and dark incubations, (2) a diel (24-h) experiment, and (3) a longer-term (4-d) carbon accumulation experiment to examine the relationship between photosynthetic rates, photosynthetic carbon metabolism in the light, and respiration and carbon metabolism in the ensuing dark period in natural assemblages of freshwater phytoplankton. High rates of photosynthesis and polysaccharide synthesis in the light were followed by high rates of respiration and polysaccharide utilization in the dark. Polysaccharide was the major respiratory substrate in the dark, and small molecular weight metabolites, lipids, and protein were less important sources of metabolic energy. The protein pool accumulated carbon during dark incubations, but more slowly than during active photosynthesis in the light. Because the intracellular macromolecular pools turn over at very different rates (polysaccharide > protein and lipid), patterns of short-term photosynthetic carbon metabolism are not necessarily indicative of the biochemical composition of the phytoplankton.

Spatial variability in the speciation and bioaccumulation of mercury in an arid subtropical reservoir ecosystem

Patterns of spatial variation of mercury and methylmercury (MeHg) were examined in sediments and muscle tissue of largemouth bass (Micropterus salmoides) from Amistad International Reservoir, a large and hydrologically complex subtropical water body in the Rio Grande drainage. The distributions of both Hg and MeHg were compared with environmental and biological factors known to influence production of MeHg. The highest concentrations of total Hg (THg) in sediment were found in the Rio Grande arm of the reservoir, whereas MeHg was highest at sites in the Devils River arm and inundated Pecos River (often more than 3.0 ng/g). Conditions in the sediments of the Devils River arm and Pecos River channel were likely more favorable to the production of MeHg, with higher sediment porewater dissolved organic carbon, and porewater sulfate levels in the optimal range for methylation. Although the detection of different groups of sulfate-reducing bacteria by polymerase chain reaction (PCR) was generally correlated with MeHg concentrations, bacterial counts via fluorescent in situ hybridization (FISH) did not correlate with MeHg. A sample of 156 largemouth bass (<30 cm) showed a spatial pattern similar to that of MeHg in sediments, where fish from the Devils River arm of the reservoir had higher muscle Hg concentrations than those collected in the Rio Grande arm. In 88 bass of legal sport fishing size (>35 cm), 77% exceeded the 0.3 mg/kg U.S. Environmental Protection Agency screening value. This study shows that significant variation in sediment MeHg and biotic Hg concentration can exist within lakes and reservoirs and that it can correspond to variation in environmental conditions and Hg methylation.

The impact of a plunging inflow on extracellular enzyme activity in a reservoir ecosystem

Reservoirs are interesting limnetic systems in that they are generally dominated by lentic conditions but can be influenced by advective processes driven by inflowing river water or by the release o f water through the dam. This combination o f conditions can produce interesting water column stratification patterns an d zonation along the length o f the reservoir ( GROEGER & KIMMEL 1984). Distinct changes in the biological communities along the length of reservoirs have frequently been observed to correspond to these zones: limited phytoplankton biomass in the up-reservoir riverine zone; peak biomass in the transitional zone; and reduced biomass down-reservoir in the lacustrine zone. Less emphasis has been placed on determining the changes in broader microbial community composition and dynamics. TIETJEN & WETZEL (2003) studied the distribution of bacterial cells, total counts, an d the proportion o f viable cells in an Alabama reservoir and found little variation along the length of the reservoir when water residence times were extremely long. Seasonal dynamics of sediment water interface bacteria were evaluated by CHRISTIAN & LIND (2007), who related bacterial substrate utilization to a suite of environmental parameters but did not consider longitudinal position. GASOL et al. (2002) considered bacterial dynamics at the longitudinal extremes of a reservoir system and found that nutrient supply was the dominant factor controlling bacterial production. Lacking in these past studies is an attempt to assess microbial community metabolism along the entire length of a reservoir encountering the changes in physical structure associated with the riverine, transitional, and lacustrine zones. To accomplish this we assayed extracellular enzyme activity from 7 sites along a 12-km transect, focusing on the changes in lake structure occurring where the inflowing river plunges under the warm surface waters ofthe lacustrine zone. This approach has been used by other researchers seeking to address different aspects of microbial activity. HARBOTT & GRAcE (2005) used extracellular enzyme activity to investigate the bioavailability of dissolved organic carbon along a gradient of urbanization, and suggested that even with stable concentrations the organic matter differences could be detected. This condition may be analogous to many reservoir systems where dissolved organic matter concentrations vary little compared to other constituents. Similarly, FINDLAY et al. (1998) used extracellular enzyme activity to characterize disso1ved organic matter in the Hudson River (New York). W e extrapolated from this approach; rather than considering organic matter composition we sought to characterize the microbial community using similar suites of enzyme activity measurements. During August 2006, Lake Dunlap reservoir in central Texas, U. S., had long water residence times, -lO days as compared to the long term average of -5.5 days, as a result of a prolonged period ofbelow normal rainfall. This established the conditions necessary for the formation of a plunge point because the cold, inflowing river water was denser than the warmer waters of the epilimnion of the reservoir. This plunging inflow produced a strong physical gradient, which was easily observed in surface chlorophyll a fluorescence and temperature patterns and clearly separated the reservoir into distinct riverine, transitional, and lacustrine zones. We investigated the impact of this physical gradient on functional attributes of the microbial community. The distinctive temperature and chlorophyll fluorescence patterns clearly identified the physical gradient (the barrier imposed by the water density gradient) and one level ofbiological gradient (the phytoplankton peak associated with the transitional zone). This research expands the understanding of kilometer-scale perturbations of the physical environment of reservoirs and how these perturbations influence, segregate, or otherwise affect the activity ofmicroorganisms.

Comparison of chemical analyses of boat and helicopter-collected water samples

Helicopters can be used to collect water samples from many lakes over a wide geographic area within a relatively short time period. Here we report the results from an experiment in which sequential water samples from a lake were collected first from a nonmotorized boat and then immediately afterward from a helicopter. No significant differences were found between the means of the measurement of 20 chemical parameters for the two methods of collection. When compared to obtaining samples from a boat, collection of samples from a helicopter platform had no effect on the content of the water samples.