Human impacts such as sewage, urban run-off, agricultural and industrial wastes are running into the marshes from nearby sources. Salt marshes are nitrogen limited and with an increasing level of nutrients entering the system from anthropogenic effects, the plant species associated with salt marshes are being restructured through change in competition. For example, the New England salt marsh is experiencing a shift in vegetation structure where "S. alterniflora" is spreading from the lower marsh where it predominately resides up into the upper marsh zone. Additionally, in the same marshes, the reed "Phragmites australis" has been invading the area expanding to lower marshes and becoming a dominant species. "P. australis" is an aggressive halophyte that can invade disturbed areas in large numbers outcompeting native plants. This loss in biodiversity is not only seen in flora assemblages but also in many animals such as insects and birds as their habitat and food resources are altered.