Tjut Sugandawaty Djohan

The use of wetlands for nutrient removal from surface runoff in a cold climate Region of California. Results from a newly constructed wetland at Lake Tahoe

Pollutant removal by wetlands represents a potential mitigation technique for treating urban runoff in the cold climates of the Sierra Nevada. This is especially encouraging in the Lake Tahoe Basin, where research has demonstrated the link between nitrate and phosphorus, and a precipitous increase of algal growth in the lake. In September 1987 a plastic-lined, gravel-filled wetland was constructed for experimental purposes and is the first demonstration of its kind in a subalpine region of the western United States. The primary objective of our research was to evaluate the effectiveness of this system in removing nitrogen, phosphorus, iron, suspended sediments and other constituents from runoff. Data collected between August 1987 and March 1989 show that the average per cent removal of total Kjeldahl-N as it passed through the wetland was low at −3%. In contrast, nitrate concentrations declined by greater than +85−90%. Changes in particulate phosphorus concentrations between inflow and outflow decreased by +47%, however, the soluble-P component showed a −28% reduction due to a contamination of the gravel during construction. The reduction of iron was very high at +84% for total reactive iron and +78% for soluble reactive iron. Finally, both turbidity and suspended solids were removed by the wetlands at an efficiency of approximately +85%.

Resistance and resilience of subalpine wetlands with respect to prolonged drought

Vegetation dynamics of subalpine wetlands in the Sierra Nevada, California, were studied from 1988 through 1996. During this period, the region experienced a drought lasting from 1988 to 1994 and reaching its extreme in 1992. Our intention was to analyze the changes in plant species diversity, composition, and biomass, and interpret them in terms of drought resistance and resilience. Four plant communities, dominated respectively byCarex rostrata, Juncus balticus, Scirpus acutus orNuphar polysepalum were clearly discernible in the marsh along the water depth gradient. Species diversity ofCarex rostrata, Scirpus acutus andNuphar polysepalum communities was the highest during the driest year, 1992, while biomass was lowest for all vegetation types in that year. Dominance ofCarex andJuncus has not changed over the years, however,Scirpus almost totally disappeared from the marsh, and theNuphar zone become dominated by the rhizomatous perennial,Hippuris vulgaris, and terrestrial ruderals in dry years. In terms of changes in species composition,Carex andJuncus communities were both resistant and resilient. TheNuphar community seemed to be less resistant and more resilient, while theScirpus community was neither resistant nor resilient. If we consider biomass per plot as a variable of interest, regardless of species composition, thenCarex andJuncus were to some extent resistant and all plots were resilient because they were able to recover quickly to their pre-drought biomass. Life histories of dominant species were a more important determinant of community stability than species diversity.

KONDISI HUTAN BAKAU TEBANGAN MASYARAKAT DAN INDUSTRI PULP DI BATU AMPAR KALIMANTAN BARAT

The purpose of this research was to study tree cutting of mangrove forest by the local people of Batu Ampar and the pulp industry at Kapuas river estuary. At each site the rapid measurement methods were established using quadrate plots of 20m x 20m and 5m x 5m, each with 2 replicates. The results revealed that the local people only cut the selective trees of Rhizophora apiculata and Bruguiera gymnorhiza with diameter of 20-25 cm2 at 0.25 ha wide, which created gap canopy as small disturbace to the mangrove forest. This area of gap canopy immediately was colonized and dominated by R. apiculata. The mangrove tree cuttings created the phase gap generations. This forest recovered quickly, thus the small distrurbance maintained the mangrove tree species diversity. The Rhizophora roots were habitat for nusery grown of larval shrimps, crabs, and fishes. The pulp industry cut all of the mangrove species wich created big disturbance and huge gap area. The forest also recovered quickly, but was dominated by Xylocarpus granatum. Thus, the big disturbance by the pulp industry caused the shifted species of the mangrove forest species from Rhizophora and Bruguiera to Xylocarpus. The roots of Xylocarpus tree were not habitat forthelarval shrimps, crabs, and fishes, which decreased the fisherman catch. The forest rehabilitation of industrial cutting was planted regularly with Rhizophora, and created many current canals which proned to the erosion. Thus the pulp industry of mangrove forest cutting threatened nursery habitat and species diversity at the mangrove forest of Batu Ampar.