The water quality of the River Wear, north-east England

A 1-year detailed study of water quality in the River Wear in combination with longer (decadal) term Environment Agency data (Harmonised Monitoring Scheme) show the influences of historic lead-zinc and coal mining and sewage inputs. The water quality for many determinands, such as sodium, chloride, boron, nitrate, and soluble reactive phosphorus, varies seasonally due to changing flow conditions. For most dissolved determinands, concentrations decrease with increasing flow in response to dilution of point and diffuse sources by rainfall. However, concentrations increase with increasing flow for dissolved organic carbon, aluminium, lead, iron, yttrium, and the lanthanides and actinides. This increase probably reflects two processes. Firstly, trace element-enriched runoff occurs from the acidic moorland areas of the catchment when it wets up. Secondly, at high flows, increased production of transition metals bearing microparticulate material occurs; these pass through conventional filters used to separate dissolved from particulate materials. For the particulate components, iron, manganese, aluminium, and some trace transition metals are present above the analytical detection limits and concentrations increase with increasing flow in response to increasing suspended sediment levels. However, particulate metal concentrations are relatively low for the Wear compared to the other eastern UK rivers, even though historic lead-zinc mining activity in the upper portions of the Wear catchment has led to extensive spoil contamination of the land. This feature probably reflects the lack of a significant flood plain area, where trace contaminants can accumulate within the sediments. The importance of inputs of pumped water from former coalmines is highlighted; increased manganese and dissolved carbon dioxide concentrations and reduced pH result. Examination of the Harmonised Monitoring Scheme data indicate no clear long-term changes in water quality for all but one determinand, although analysis is hampered by changes in sampling frequency for all determinands and changes in detection limits for certain trace metals. The only clear long-term change is a reduction in the micro-organic insecticide, aldrin. Nonetheless, the long-term data, when plotted as a function of month, follow the same pattern as the LOIS data. For aldrin, the higher values during the early period of record occurred in the latter half of each year, presumably as a consequence of seasonal application and enhanced leaching during the autumn.

Phosphatase Activities of Endolithic Communities in Rocks of the Antarctic Dry Valleys.

Phosphorus is scarce in Beacon Sandstone of the McMurdo Dry Valleys, Antarctica, and any input from precipitation is minimal. In endolithic microbial communities recycling of P by the action of phosphatases may therefore be important. The phosphatase activities of three different types of endolithic communities in the McMurdo Dry Valley, Antarctica, were studied in the laboratory. The dominant phototrophs were Chroococcidiopsis, mixed Gloeocapsa and Trebouxia, and Trebouxia. Bacteria were also visually conspicuous in the latter two communities, and the Trebouxia in both cases formed a lichenized association with fungal hyphae. In each case marked phosphomonoesterase (PMEase) activity was found in assays with 4-methylumbelliferyl phosphate (MUP) or p-nitrophenyl phosphate as substrate, and phosphodiesterase activity with bis-p-nitrophenyl phosphate as substrate. The pH optimum of PMEase (assayed at 0.5 pH intervals) of the Chroococcidiopsis, Gloeocapsa-Trebouxia, and Trebouxia communities was 9.5, 5.5, and 8.0, respectively. These values are similar for aqueous extracts of the respective rocks (pH 9.2, 6.2, 7.5). All three communities showed significantly higher PMEase activity at 5 degrees than 1 degrees C, and the first two also showed much higher activity at 5 degrees than 10 degrees C. All three communities also showed slightly lower activity in the light (7 µmol photon m(-2) s(-1)) than the dark; this was found with all substrates and substrate concentrations. Prior exposure of a moistened sample to light for 2 h led to a reduction in activity even when the subsequent assay was done in the dark. The rate of PMEase activity (using 100 µM MUP) in the Gloeocapsa-Trebouxia and Trebouxia communities was approximately linear with time up to 24 h, whereas the Chroococcidiopsis community showed a marked decrease after 6 h. At least part of this was due to retention of the 4-methylumbelliferone (MU) hydrolysis product. In spite of the assays being conducted on a whole community, the activity-substrate relationship in each case quite closely resembled a typical Michaelis-Menten relationship. Estimates were made of the apparent half-saturation value and the concentration of MUP required to support half-maximal rates. The apparent K (m) values were: Chroococcidiopis, 230 µM; Gloeocapsa-Trebouxia 169 µM; Trebouxia, 135 µM. The respective values for apparent V (max) were 0.053, 0.55, and 0.35 µmol MU g(-1) h(-1). In view of the greater dependence of these communities on the rock for their sole supply of P than for C and probably N, it is suggested that the cycling of P within the communities is a key factor influencing their overall metabolic activity when moisture permits their activation.

Kinetic Parameters of Denitrification in a River Continuum.

Kinetic parameters for nitrate reduction in intact sediment cores were investigated by using the acetylene blockage method at five sites along the Swale-Ouse river system in northeastern England, including a highly polluted tributary, R. Wiske. The denitrification rate in sediment containing added nitrate exhibited a Michaelis-Menten-type curve. The concentration of nitrate for half-maximal activity (Kmap) by denitrifying bacteria increased on passing downstream from 13.1 to 90.4 µM in the main river, but it was highest (640 µM) in the Wiske. The apparent maximal rate (Vmaxap) ranged between 35.8 and 324 µmol of N m-2 h-1 in the Swale-Ouse (increasing upstream to downstream), but it was highest in the Wiske (1,194 µmol N m-2 h-1). A study of nitrous oxide (N2O) production at the same time showed that rates ranged from below the detection limit (0.05 µmol of N2O-N m-2 h-1) at the headwater site to 27 µmol of N2O-N m-2 h-1 at the downstream site. In the Wiske the rate was up to 570 µmol of N2O-N m-2 h-1, accounting for up to 80% of total N gas production.