Academic literature on the topic 'Epilithon production'

Techniques are presented for the measurement of bacterial production (by the rate of 3H-TdR incorporation into DNA), isotope dilution, time course of incorporation of nucleoside, and disturbance artifacts in natural epilithic (on rock) communities of headwater streams. The epilithon in riffles was subsampled by carefully chipping upper rock surfaces. Chips were placed in test tubes and incubated in situ. Test tubes were rotated to reduce the formation of artificial diffusion barriers to TdR transport. DNA was isolated using a double filtration technique. Summertime production had a range of 1.3–51 mg C∙m−2∙h−1 in five southern Ontario streams. Precursors to DNA synthesis, which diluted 3H-TdR, had a range of 63–440 nM. Incorporation of 3H-TdR was linear for at least 1 h. Disturbance artifacts did not appear from rock chipping or from extended sample rotation. The techniques can be applied to other microbial groups from various aquatic hard substrata.

Bacterial abundance, biomass, and heterotrophic production were measured in the water, sediment, and epilithon of forested and open streams in southern Ontario in summer 1988. Relationships of environmental variables to production were examined. The time course of nucleoside incorporation, recovery efficiency of bacterial DNA, isotope dilution, and disturbance artifacts were examined to compare bacterial production rates and to determine the appropriateness of the rate of [3H]thymidine incorporation into bacterial DNA as an estimate of bacterial production in these habitats. Water column bacterial biomass (12–97 μg C∙L−1) and heterotrophic production (0.21–67 μg C∙L−1∙h−1) were greater in open streams than in forested streams. Differences between open and forested stream sediment bacterial biomass (0.30–1.1 g C∙m−2) and heterotrophic production (18–140 mg C∙m−2∙h−1) were not as pronounced as they were in the water column. A methodological disturbance artifact may have introduced a minor bias in sediment production measurements. Epilithic bacterial biomass was 35–150 mg C∙m−2, and heterotroph production was 1.3–51 mg C∙m−2∙h−1, significantly greater (P < 0.05) in open streams than in forested streams. Epilithic production and stream water temperature were positively correlated (P < 0.05). Heterotrophic bacterial production exceeded net primary production in forested streams, but not in open streams.

We examined the dependence of epilithic algal standing crop, production, and nutrient limitation upon water column nutrients in 12 softwater lakes of northeastern Pennsylvania. Elevated dissolved inorganic nitrogen accompanied low dissolved inorganic carbon in the more acidic lakes, while P varied little within the study area. The growth of epilithon on clay flower pot substrata diffusing combinations of N (NaNO3), P (Na2HPO4), and C (NaHCO3) was compared with growth on control substrata to evaluate which of the three nutrients limited growth in each lake. Standing crop accrual as chlorophyll a on control substrata averaged 0.8 μg/cm2, with little variation among lakes. Nutrient limitation of growth, however, was strongly related to lake alkalinity. Chlorophyll a was typically enhanced by N and/or P only in lakes with alkalinity greater than ~100 μeq/L and responded strongly to C enrichment in the two most acidic lakes. Combined addition of all three nutrients produced the largest chlorophyll a accrual in all 12 lakes. Invertebrate grazer biomass, dominated by chironomids in the more acidic lakes and by snails at higher alkalinity, was negatively related to chlorophyll a on these NPC substrata (r = −0.57, p = 0.05) and may have reduced algal standing crop well below nutrient-sustainable levels in some lakes.

Patterns of epilithic algal and bacterial productivity were examined in a developing community on newly exposed stream bedrock for a period of 10 wk and in an undisturbed bedrock community used as a seasonal control. Physical and chemical changes were minimal over the experimental period. Bacterial colonization occurred initially and was rapidly followed by the development of a monolayer of adnate diatoms. Subsequent bacterial development coupled with maximum rates of bacterial productivity may have depended upon the algal cells for physical refugia, mucilage production, and/or other growth-promoting substrates present in algal photosynthate. After the diatom monolayer, filamentous algae developed despite the presence of high densities of snail grazers. By the end of the experiment, community composition on both substrata was generally similar although filamentous blue-green algae were a more important component of the native communities. Communities on newly exposed rock had higher total levels of epilithic productivity than on native rock where bacterial numbers averaged 2.26 × 1011 cells/m2. On native rock epilithic bacterial productivity averaged 72 mg C∙m−2∙d−1, yielding an average turnover time of 0.56 d; algal productivity averaged 224 mg C∙m−2∙d−1. These data suggested that epilithic production was not quantitatively limiting as a food resource for grazing snails in this stream during the summer months.

We used natural variation in sockeye salmon (Oncorhynchus nerka) spawner biomass among sites and years in three undisturbed, forested watersheds in interior British Columbia to test the hypotheses that salmon were a major source of particulate organic matter inputs to the streams and that carcass biomass determined stream-water nutrient concentrations and epilithic algal production. Sockeye carcasses were retained at the spawning sites, primarily (75–80%) by large woody debris (LWD) or pools formed by LWD. The abundance and distribution of sockeye salmon determined stream-water nutrient concentrations and epilithic chlorophyll a concentrations during late summer and early fall when most primary production occurred in the oligotrophic streams. Periphyton accrual rates were elevated at sites with high salmon biomass. Peak chlorophyll a concentration increased with increasing carcass biomass per unit discharge above a threshold value to reach maxima 10-fold greater than ambient levels. Epilithic algae were dominated by a few common, large diatom taxa. Salmon carcasses were the dominant source of particulate organic carbon in low gradient stream reaches. Nutrient budget modeling indicated that most of the salmon-origin nutrients were exported from the spawning streams or removed to the terrestrial ecosystem; diffuse impacts may extend over a much larger area than simply the sites used for spawning.

There is limited knowledge and understanding of the role of nutrients and effect of herbivore grazing on epilithon production in Australian upland rivers. Before investigating these processes, a method was required that will allow the study of factors (physical, chemical and biological) that affect epilithon abundance and distribution in lotic systems. The Thredbo River, Kosciusko National Park, New South Wales, provided an opportunity to conduct this investigation because it: is relatively undisturbed; has been intensely studied; is easily accessed; and is of appropriate width and depth to conduct in-stream experiments. The specific goals of this research were the: (1) validation of the nutrient-diffusing substrate method for investigating epilithon responses to nutrients; (2) development of experimental channels in which to investigate nutrient/epilithon dynamics in an upland stream; (3) development of a method to inhibit macroinvertebrate grazing from in situ experimental channels, so that epilithon responses to nutrients with and without grazing pressure can be studied; and (4) assessment of the ecological implications of nutrient/ epilithon/macroinvertebrate interactions assessed from in-stream experiments. Major achievements of my research, that advance the study of stream ecology, are as follows: · The investigation of the features of nutrient release from terracotta nutrientdiffusing substrates showed that phosphorus does not readily diffuse through terracotta clay, probably because terracotta contains known binding agents for phosphorus, such as iron, and because pores are easily blocked. I concluded that this type of substrate is inappropriate for studying nutrient dynamics and epilithon responses to the nutrient(s) limiting growth. The outcomes of this research has implications for future research using nutrient-diffusing substrates, and of how nutrient limitation information is interpreted from past research using terracotta nutrient-diffusing substrates. · I designed and tested in-stream experimental channels that were functional and provided near natural conditions for studying the interactions between nutrients/ epilithon/macroinvertebrates, without affecting physical variables not tested for. The in situ method developed was successful in simulating 'real world' complexities. Clay paving bricks were used as standardized common surface for community development because their colour, size and surface texture are similar to those of natural stones. · I developed a technique for successfully inhibiting macroinvertebrate grazing from designated areas, using electricity, without affecting flow and light. This technique will enable in-stream herbivory studies to assess the effects of macroinvertebrate grazing pressure on epilithon under natural conditions, including variability in flow, temperature, light and nutrients. It will allow the vexed question of whether epilithon biomass is controlled by bottom-up or top-down processes to be objectively addressed. The construction of in situ experimental channels that simulate natural conditions, combined with the non-intrusive methods of macroinvertebrate exclusion and nutrient addition, resulted in a study design that will facilitate the investigation of biotic responses to nutrients in Australian upland streams. Using the method developed, I showed that variable flows in the upper Thredbo River appear high enough to slough epilithon, but not high enough to dislodge macroinvertebrates. This may mean that in systems such as the Thredbo River that experience frequent low level disturbance, the epilithon is unable to reach equilibrium. There is strong top-down control of epilithon in this stream, with nutrients, temperature and light playing a secondary role. I concluded that natural variability may be more important than previously considered and perhaps this, rather than constancy, should be studied. This thesis adds support to the continuance of multiple factor investigations, and advocates that such studies be conducted under natural conditions so that the results are more relevant to natural systems than from studies conducted in controlled laboratory and outdoor artificial streams. Clearly, the in-stream channels, developed as part of the current research, will allow research that contributes to our understanding of community responses to the physical, chemical and biological processes operating in lotic environments.

Biological processes form the basis for a rich source of information for paleolimnologists. Populations of organisms are sensitive to variations in their external environment, and this sensitivity can be recorded as proportional changes in fossil abundances, evolutionary change, or extinction. Variations in lake temperature or water chemistry below the threshold of geochemical archives would normally go unrecorded in lake deposits were it not for fossils capable of registering these changes. Biotic systems are also the most complex components of lake systems, involving numerous species, their interactions with each other, and with their external environment. As a result, the interpretation of lacustrine fossil records is rarely straightforward, and must be viewed in the context of complex ecological dynamics, unfolding against a background of environmental and evolutionary change. In this chapter we will consider the biotic structure of lakes from a paleolimnological perspective, focusing on organisms and ecological interactions likely to be preserved in a lake’s fossil record. A transect running downslope and offshore from the shoreline will almost invariably reveal a change in habitat and lake organisms (see figure 3.2). In the shallow, littoral zone, high rates of photosynthesis can normally be supported, as light is not a limiting factor for growth. A high diversity of autotrophic and heterotrophic (consuming) organisms is encountered here. Near the shoreline, a fringe of emergent or submerged macrophytes is often present, either attached to the substrate, or floating nearshore. These plants form a substrate for many attached (epiphytic) or crawling organisms. On wave-swept, rocky, or sandy coasts macrophytes may be absent, but abundant algae or photosynthetic bacteria may be present, attached to rock surfaces (epilithic), or adhering to sand grains. In the sublittoral zone, light penetration is reduced, and large macrophytic plants are absent, but lower levels of benthic primary production may persist from algal or bacterial growth. Although algae are frequently found below the photic zone, because of circulation or settling, they are not photosynthesizing under such conditions. In the aphotic, profundal zone food resources are provided exclusively through secondary productivity, consumption of settling detritus (or the organisms that feed on such detritus), and microbial food resources.