Atmospheric carbon dioxide: its role in maintaining phytoplankton standing crops

The rate of invasion of carbon dioxide into an artificially eutrophic Canadian Shield lake with insufficient internal sources of carbon was determined by two methods: measuring the carbon : nitrogen : phosphorus ratios of seston after weekly additions of nitrogen and phosphorus, and measuring the loss of radon-222 tracer from the epilimnion. Both methods gave an invasion rate of about 0.2 gram of carbon per square meter per day. The results demonstrate that invasion of atmospheric carbon dioxide may be sufficient to permit eutrophication of any body of water receiving an adequate supply of phosphorus and nitrogen.     

Current and historical inputs of mercury to high-latitude lakes in Canada and to Hudson Bay

Sediment cores collected from several lakes in northern Canada have been analyzed for mercury and several other chemical contaminants. Sites ranged from the Experimental Lakes Area of northwestern Ontario, north to Cornwallis Island, and west to the southern Yukon. Cores were sliced at sites of collection and individual slices were freeze dried and analyzed for Pb-210 and Cs-137 to estimate average time intervals of deposition. The earliest date estimated by Pb-210 was about 1850, and mercury concentrations in some lakes were clearly increasing before then, assuming no vertical movements of mercury within the sediments. Extrapolation of dates downward to deeper slices, assuming a constant sedimentation rate, indicated that in some lakes mercury inputs increased slowly even in the 1500's, more rapidly after 1750, and more rapidly yet over the current century. These increases are interpreted as increased fluxes of mercury to the lakes as a result of long-range transport of atmospheric mercury, since there are no local industrial sources of mercury. Slices taken near the bottom of a core are taken to estimate the geological component while elevations in excess of that in surface slices are taken to represent contamination from fallout. This partitioning suggests that sediments in the eastern Northwest Territories are dominated by pollution, while those from the western Northwest Territories are influenced more by their geological settings. Two cores from Hudson Bay suggest that mercury is increasing there too, but has not yet exceeded geological sources. Mercury shows little or no tendency to decline in the most recent slices; indicating that inputs of mercury remain at or near their historical maxima. Given relatively high and continuing inputs of mercury to northern lakes it seems likely that some portion of that mercury may find its way into the food chain, hence the long-term prospect is for increasing levels of mercury in northern fish.     

Inorganic sediment budget in the mangrove-fringed Fly River Delta,Papua New Guinea

Six oceanographic moorings were maintained for 8 weeks across the mouth of the mangrove-fringed Fly River estuary from April to June 1995 in the southeast trade wind season. A further 4 moorings were deployed for 8 weeks along the estuary channel in 1992, also in the southeast trade wind season. These data were used to estimate net exchange of suspended sediment between the estuary and the Gulf of Papua. A net inflow of fine sediment into the estuary from the coastal ocean was found to be considerable, about 40 tonnes s^-1 or about 10 times the riverine inflow rate, resulting in a calculated, spatially averaged vertical accretion rate of 2 mm year^-1. Mangroves may account for trapping 6% of the riverine sediment inflow or about 1/4 of the riverine clay inflow. If this sediment was distributed only over the observed accumulation zones near islands the local accumulation rates in these zones would reach 4 cm year^-1. Estimates of soft sediment mass accumulation rates (1–10 kg m^-2 year^-1) in the channel from Pb-210 and C-14 measurements from cores of deltaic mangrove mud cannot account for this accumulation rate on a 100–1000 year time scale. The fate of the remaining sediment is unknown, it may be exported from the estuary in the monsoon season.     

Water,salt and nutrient fluxes of tropical tidal salt flats

The water budget of a tropical tidal salt flat in dry tropical Australia has been studied with particular emphasis on estimating the groundwater fluxes. Salt was used as a passive tracer to determine some of these fluxes. Groundwater salt accumulation (or loss) was less than 1 kg/m³/month. Surface water leaving the flat at a higher salt concentration than flood water causes a net outwelling of salt of between 0.4 and 1 kg/m²/month. Evaporation from the salt flat was estimated to be 70 mm/month. Using these measurements and a simple model of the groundwater flows, it is concluded that the groundwater loss is less than 40 mm/month. The accuracy of the salt budget was insufficient to rule out the possibility that the net groundwater motion was upwards. Measurements of Si and PO_{_4} fluxes indicated that the net outwelling due to surface water flows were respectively 3 mmole/m²/month and 0.014 mmole/m²/month. A net groundwater loss of 10 mm would produce a similar magnitude outwelling due to groundwater discharge. The mangrove-fringed tropical tidal salt flats are the source of large quantities of nutrients that are released to the near-shore zone.     

Sources,sinks, and export of organic carbon through a tropical,semi‐enclosed delta (Hinchinbrook Channel,Australia)

A mass balance for organic carbon in Hinchinbrook Channel was constructed to identify major sources, sinks, and the magnitude of organic matter available for export to the adjacent coastal zone. Total organic carbon input from the Herbert River and from net production of mangroves, phytoplankton, seagrasses, and benthic microalgae is 8.94 ×109M Corgyr–1 (moles organic carbon per year). Mangroves and river inputs are the largest carbon sources, accounting for 56% and 27% of the total annual input, respectively. Benthic respiration and burial in sediments are the major sinks, accounting for 46% and 41% respectively of total losses (3.09 ×109 M Corgyr–1). This mangrovedominated coastal ecosystem is net autotrophic, with 5.85×109M Corgyr–1 (65% of total Corg input) available for export to the adjacent nearshore zone. Total export of organic carbon from the region (adding carbon export from Missionary Bay mangroves on the northern end of Hinchinbrook Island) amounts to 82,800 metric tons of organic carbon per year. These results confirm earlier evidence indicating that much of the particulate sediment carbon in the adjacent coastal zone is of mangrove origin. This mass balance, although preliminary, demonstrates the importance of Hinchinbrook Channel as a source of organic matter for the Great Barrier Reef lagoon.