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Greenhouse mesocosms of freshwater marsh vegetation were exposed to a simulated saltwater intrusion event followed by a recovery period during which water levels and interstitial water salinity were adjusted over a range of conditions. Virtually all above-ground vegetation, including the three dominant species, Sagittaria lancifolia L., Leersia oryzoides (L.) Swartz, and Panicum hemitomon Schultes, was killed by the initial saltwater intrusion event. P. hemitomon did not recover, but S. lancifolia and L. oryzoides, as well as many of the other species initially present, exhibited some ability to recover depending on post-saltwater intrusion conditions. Increasingly harsh recovery conditions (for freshwater marsh vegetation), including more reduced soil conditions, higher interstitial salinities, and higher interstitial sulfide concentrations were associated with decreased live above-ground biomass and species richness. The effect of elevated salinity on vegetative recovery became more pronounced under flooded conditions. This experiment illustrates that the response of a freshwater marsh community to the long-term disturbance effect of a transient saltwater intrusion event will be strongly influenced by post-intrusion salinity and water levels.

We investigated physiological integration among ramets of Spartina patens when clones spanned a salinity gradient. Clones of S. patens were grown in paired pots with the ramets of the parent pot connected to the ramets of the daughter pot via a common rhizome. Half of these clones had the rhizome connection between parent and daughter pots severed immediately prior to treatment application. The parent pots were kept at low salinity (34.2 mM NaCl) and given two levels of labeled 15NH4Cl (0.036 or 0.714 mM NH4Cl). Daughter ramet pots were kept at the low N level (unlabeled 0.036 mM NH4Cl) and exposed to an increase in salinity to 513 mM NaCl. After 7 days, all daughter ramets had significantly elevated leaf Na levels. Daughter ramets connected to parents were able to maintain significantly greater leaf elongation rates than severed daughter ramets. Labeled 15N was translocated from parents to connected daughter ramets and high-N parents translocated more N to the belowground tissue of daughter ramets than low-N parents. Leaf proline, a nitrogen-containing osmoticum that accumulates only after a threshold of salinity stress is exceeded, was significantly increased only in severed daughter ramets, indicating that salinity stress was reduced in connected daughter ramets, possibly via parental water translocation. Key words: clone, physiological integration, proline, ramet, salt marsh, salt stress.

/ Land-use activities affect water quality by altering sediment, chemical loads, and watershed hydrology. Some land uses may contribute to the maintenance of water quality due to a biogeochemical transformation process. These land-use/land-cover types can serve as nutrient detention zones or as nutrient transformation zones as dissolved or suspended nutrients or sediments move downstream. Despite research on the effects of individual land-use/land-cover types, very little has been done to analyze the joint contributions of multiple land-use activities. This paper examines a methodology to assess the relationships between land-use complex and nitrate and sediment concentrations [nonpoint source (NPS) pollutants] in streams. In this process, selected basins of the Fish River, Alabama, USA, were delineated, land-use/land-cover types were classified, and contributing zones were identified using geographic information system (GIS) and remote sensing (RS) analysis tools. Water samples collected from these basins were analyzed for selected chemical and physical properties. Based on the contributions of the NPS pollutants, a linkage model was developed. This linkage model relates land use/land cover with the pollution levels in the stream. Linkage models were constructed and evaluated at three different scales: (1) the basin scale; (2) the contributing-zone scale; and (3) the stream-buffer/riparian-zone scale. The contributing-zones linkage model suggests that forests act as a transformation zone, and as the proportion of forest inside a contributing zone increases (or agricultural land decreases), nitrate levels downstream will decrease. Residential/urban/built-up areas were identified as the strongest contributors of nitrate in the contributing-zones model and active agriculture was identified as the second largest contributor. The regression results for the streambank land-use/land-cover model (stream-buffer/riparian-zone scale) suggest that water quality is highest when passive land uses, such as forests and grasslands, are located adjacent to streams. Nonpassive land uses (agricultural lands or urban/built-up areas) located adjacent to streams have negative impacts on water quality. The model can help in examining the relative sensitivity of water-quality variables to alterations in land use made at varying distances from the stream channel. The model also shows the importance of streamside management zones, which are key to maintenance of stream water quality. The linkage model can be considered a first step in the integration of GIS and ecological models. The model can then be used by local and regional land managers in the formulation of plans for watershed-level management. KEY WORDS: Water quality; Land-use complex; Geographic information system; Nonpoint source pollution; Forested buffers

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