Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.

Distribution and sources of particulate organic matter in the water column and sediments of the Fly River Delta, Gulf of Papua (Papua New Guinea)

Abstract: Suspended particles from surface and bottom waters and surficial sediments from the seabed were collected throughout the Fly River subaqueous delta region during the monsoon season in January 2003. Because of the unusually low river discharge associated with a strong El Nino, water-column salinities were relatively high (10 to 32) throughout most of the delta, with brackish salinities ( 4 wt.%), relatively high organic carbon:nitrogen molar ratios (OC:N > 20 mol:mol) and quite depleted stable isotopic compositions of organic carbon (δ13COC < −27‰). In contrast, surface sediments in the seabed displayed spatially uniform compositions that were characterized by markedly lower %OC contents (1.1 ± 0.8 wt.%), lower OC:N ratios (17 ± 9 mol:mol) and relatively enriched δ13COC compositions (−25.5 ± 1.1‰). The radioisotopic compositions of OC from a selected set of seabed samples (Δ14COC of −408 ± 82‰) indicate OM in surface sediments is old (14C ages of 2800 to over 6000 years before present). The ratios of organic carbon to mineral surface area exhibited by these sediments are within the typical (mono-layer equivalent) ranges characteristic of shelf sediments and do not reflect the preferential removal of terrigenous OM. Overall, these compositions indicate that while water-column POM appears to be derived mainly from terrigenous vascular plant debris and riverine/estuarine phytoplankton, the source of most of the sedimentary POM is aged, soil OC ultimately derived from C3 vegetation. We speculate that the concentrations and sources of suspended POM in the water column of the Fly River delta region reflect the conditions of low river discharge, low wave energy and neap tides encountered at the time of sampling. In contrast, POM compositions in surface sediments are consistent with the transport and deposition of old, mineral-bound OC most likely eroded from the upland regions of the Fly River watershed, which is characterized by steep slopes, high precipitation and C3 tropical forests and grasslands.

Forest harvest impacts on water quality and aquatic biota on the Boreal Plain: introduction to the TROLS lake program

Abstract: Eleven headwater lakes in Alberta's Boreal Plain were monitored for nutrients and plankton 2 years before and 2 years after variable watershed harvesting (harvesting mean 15%, range 0-35%). After harvesting, variations in annual precipitation resulted in lake water residence times that differed by an order of magnitude from one year to the next. During the first posttreatment year, total phosphorus concentrations increased (overall 40%) in most lakes; how - ever, response was most consistent in lakes that were shallow and the water column mixed or weakly thermally strati- fied. Chlorophyll a, cyanobacteria (Aphanizomenon-Anabaena), and cyanotoxins (microcystin-LR) increased after harvesting, primarily in shallow lakes. Zooplankton abundance and biomass decreased after harvesting, particularly in stratified lakes where edible phytoplankton biomass declined. In the weakly or nonstratified lakes, declines in zooplank - ton biomass were associated with higher cyanobacterial biomass and cyanotoxins. Posttreatment change in total phos- phorus concentration was strongly related to weather (greatest response in a wet year) and relative drainage basin size (drainage basin area to lake volume, r 2 = 0.78, P << 0.01). There was no evidence that buffer strip width (20, 100, and 200 m) influenced lake response. These results suggest that activities within the entire watershed should be the fo - cus of catchment-lake interactions.

Benthic nutrient remineralization in a coastal lagoon ecosystem

Abstract: In situ measurements of the exchange of ammonia, nitrate plus nitrite, phosphate, and dissolved organic phosphorus between sediments and the overlying water column were made in a shallow coastal lagoon on the ocean coast of Rhode Island, U.S.A. The release of ammonia from mud sediments in the dark (20–440 μmol per m2 per h) averaged ten times higher than from a sandy tidal flat (0–60 μmol per m2 per h), and while mud sediments also released nitrate and phosphate, sandy sediments took up these nutrients. Fluxes of nutrients from mud sediments, but not from sandy areas, markedly increased with temperature. Ammonia release rates for mud sediments in the light (0–350 μmol per m2 per h) were lower than those in the dark and it is estimated that some 25% of the ammonia released to the water column on an annual basis may be intercepted by the benthic microfloral community. Estimates of the annual net exchange of nutrients across the sediment-water interface, weighted by sediment type for the lagoon as a whole, showed a release of 450 mmol per m2 of ammonia, 5 mmol per m2 of phosphate, 5 mmol per m2 of dissolved organic phosphorus, and an uptake of 80 mmol per m2 of nitrate. Although rates of ammonia and nitrate exchange were comparable to those described for the deeper heterotrophic bottom communities of nearby Narragansett Bay, rates of benthic phosphate release were significantly lower. On an annual basis the Bay benthos released approximately 20 times more inorganic phosphate per unit area than did the lagoon benthos. As a result., the N/P ratio for the flux from the sediments was 74∶1 in the lagoon, compared with 16∶1 in “average” marine plankton and 8∶1 for the benthic flux from Narragansett Bay. The lack of remineralized phosphate in the lagoon, is reflected in water, column phosphate concentrations (always <1 μm) and water column N/P ratios (annual N/P=27) and suggests that the lagoon may show phosphate limitation rather than the nitrogen limitation commonly associated with marine systems.