Ash-free Dry Mass (ash-free + dry_mass)

Distribution by Scientific Domains

Selected Abstracts

Exoenzyme activities as indicators of dissolved organic matter composition in the hyporheic zone of a floodplain river

Summary 1. We measured the hyporheic microbial exoenzyme activities in a floodplain river to determine whether dissolved organic matter (DOM) bioavailability varied with overlying riparian vegetation patch structure or position along flowpaths. 2. Particulate organic matter (POM), dissolved organic carbon (DOC), dissolved oxygen (DO), electrical conductivity and temperature were sampled from wells in a riparian terrace on the Queets River, Washington, U.S.A. on 25 March, 15 May, 20 July and 09 October 1999. Dissolved nitrate, ammonium and soluble reactive phosphorus were also collected on 20 July and 09 October 1999. Wells were characterised by their associated overlying vegetation: bare cobble/young alder, mid-aged alder (8,20 years) and old alder/old-growth conifer (25 to >100 years). POM was analysed for the ash-free dry mass and the activities of eight exoenzymes (,-glucosidase, ,-glucosidase, , -N-acetylglucosaminidase, xylosidase, phosphatase, leucine aminopeptidase, esterase and endopeptidase) using fluorogenic substrates. 3. Exoenzyme activities in the Queets River hyporheic zone indicated the presence of an active microbial community metabolising a diverse array of organic molecules. Individual exoenzyme activity (mean ± standard error) ranged from 0.507 ± 0.1547 to 22.8 ± 5.69 ,mol MUF (g AFDM),1 h,1, was highly variable among wells and varied seasonally, with the lowest rates occurring in March. Exoenzyme activities were weakly correlated with DO, DOC and inorganic nutrient concentrations. 4. Ratios of leucine aminopeptidase : ,-glucosidase were low in March, May and October and high in July, potentially indicating a switch from polysaccharides to proteins as the dominant component of microbial metabolism. 5. Principal components analysis indicated that there were patch effects and that these effects were strongest in the summer. 6. DOM degradation patterns did not change systematically along hyporheic flowpaths but varied with overlying forest patch type in the Queets River hyporheic zone, suggesting that additional carbon inputs exist. We hypothesise that the most likely input is the downward movement of DOM from overlying riparian soils. Understanding this movement of DOM from soils to subsurface water is essential for understanding both the hyporheic metabolism and the carbon budget of streams and rivers. [source]

Stream food web response to a salmon carcass analogue addition in two central Idaho, U.S.A. streams

Summary 1. Pacific salmon and steelhead once contributed large amounts of marine-derived carbon, nitrogen and phosphorus to freshwater ecosystems in the Pacific Northwest of the United States of America (California, Oregon, Washington and Idaho). Declines in historically abundant anadromous salmonid populations represent a significant loss of returning nutrients across a large spatial scale. Recently, a manufactured salmon carcass analogue was developed and tested as a safe and effective method of delivering nutrients to freshwater and linked riparian ecosystems where marine-derived nutrients have been reduced or eliminated. 2. We compared four streams: two reference and two treatment streams using salmon carcass analogue(s) (SCA) as a treatment. Response variables measured included: surface streamwater chemistry; nutrient limitation status; carbon and nitrogen stable isotopes; periphyton chlorophyll a and ash-free dry mass (AFDM); macroinvertebrate density and biomass; and leaf litter decomposition rates. Within each stream, upstream reference and downstream treatment reaches were sampled 1 year before, during, and 1 year after the addition of SCA. 3. Periphyton chlorophyll a and AFDM and macroinvertebrate biomass were significantly higher in stream reaches treated with SCA. Enriched stable isotope (,15N) signatures were observed in periphyton and macroinvertebrate samples collected from treatment reaches in both treatment streams, indicating trophic transfer from SCA to consumers. Densities of Ephemerellidae, Elmidae and Brachycentridae were significantly higher in treatment reaches. Macroinvertebrate community composition and structure, as measured by taxonomic richness and diversity, did not appear to respond significantly to SCA treatment. Leaf breakdown rates were variable among treatment streams: significantly higher in one stream treatment reach but not the other. Salmon carcass analogue treatments had no detectable effect on measured water chemistry variables. 4. Our results suggest that SCA addition successfully increased periphyton and macroinvertebrate biomass with no detectable response in streamwater nutrient concentrations. Correspondingly, no change in nutrient limitation status was detected based on dissolved inorganic nitrogen to soluble reactive phosphorus ratios (DIN/SRP) and nutrient-diffusing substrata experiments. Salmon carcass analogues appear to increase freshwater productivity. 5. Salmon carcass analogues represent a pathogen-free nutrient enhancement tool that mimics natural trophic transfer pathways, can be manufactured using recycled fish products, and is easily transported; however, salmon carcass analogues should not be viewed as a replacement for naturally spawning salmon and the important ecological processes they provide. [source]

Particulate Organic Matter (POM) in the Humid and Wet Zones of the Ellegirini River, Kenya

Charles Mwithali M'Erimba
Abstract Field experiments to quantify the amount of particulate organic matter as an energy source for the system were conducted between February 2002 and June 2002 in humid and wet zones of the Ellegirini River in Kenya. The experiment involved collecting ten random samples from each zone. The humid zone held a hundred times more coarse particulate organic matter (CPOM) ash-free dry mass than the wet zone, where the stream current and other influencing parameters decreased CPOM amount. In conclusion it can be said that these significant differences are the result of different attributes between these two zones. Factors like current velocity, discharge or the absence of CPOM holding structures are responsible for low CPOM in the wet zone. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Abundance, Population Structure and Production of Scrobicularia plana and Abra tenuis (Bivalvia: Scrobicularidae) in a Mediterranean Brackish Lagoon, Lake Ichkeul, Tunisia

Caterina Casagranda
Abstract Abundance, growth and production of the deposit-feeding bivalves were studied in the Ichkeul wetland, northern Tunisia, from July 1993 , April 1994. Scrobicularia plana(Da Costa, 1778) occurred at annual mean densities (biomasses) of 299 ± 65 to 400 ± 100 individuals/m2 (22.54 ± 3.00 to 34.27 ± 3.96 g ash-free dry mass (AFDM)/m2) depending on the study area. The annual mean density of Abra tenuis(Montagu, 1803) amounted to 640 ± 74 individuals/m2 during the whole study period, in contrast the biomass rose from 2.87 g AFDM/m2 in July to 10.29 g AFDM/m2 in April. Both species were largely dominated by age class I. Although not very successful, recruitment presented a two-period pattern: the main period at the beginning of spring, and a secondary one in late summer/autumn. S. plana rarely exceeded 40 mm and lived for only 2 years, while most individuals of A. tenuis lived for only 15,18 months growing to a length of 12 mm. The annual bivalve deposit-feeder production for the whole lagoon system (90 km2) was 8.24 g AFDM/m2 (5.26 g C/m2, 0.65 g N/m2). The annual P/ ratio was about 0.4 and therefore in the same order of magnitude as estimates from other brackish coastal waters. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Experimental Analysis of Grazing by the Mayfly Meridialaris chiloeensis on Different Successional Stages of Stream Periphyton

Verónica Díaz Villanueva
Abstract In this study we determined grazing effects of the South Andean endemic mayfly Meridialaris chiloeensis on periphyton at different stages of successional development. Grazing effects were studied through a two-factor experimental design (colonization stages X grazer density) in a stream-side channel in spring and winter. Our results showed an absence of proportionality between grazer density and periphyton decline in response to grazers at low and intermediate levels of periphytic biomass; however, when periphyton biomass was high a direct inverse relationship was observed between post-grazing biomass and grazer density. The relationship between periphytic algae (chlorophyll a concentration) and periphyton (total periphytic ash-free dry mass) (C/OM index) was used as an estimation of the autotrophic fraction in the total periphyton matrix. Grazing did not alter the C/OM index indicating that both autotrophic and heterotrophic fractions of the periphyton components were reduced in the same proportion. Ordination of samples using the relative abundance of diatom species showed that herbivore effect was less evident at intermediate and late stage of colonization than at early one. These results support the statement that the outcome of the herbivore-periphyton interaction may depend on the successional stage of the periphyton community. In spring Fragilaria pinnata relative abundance, on the basis of cell counts, was reduced by grazing and Nitzschia palea was enhanced. In the winter experiment, grazing decreased Achnanthes minutissima relative abundance. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]