Ecological and social connectivity in an urban river system

Background/Question/Methods

Urbanization of watersheds leads to unique situations in which ecological and informational flow can be impeded or altered by physical and jurisdictional barriers. We studied the ecological and social connectivity of the Rahway River Watershed, New Jersey. The Rahway River watershed encompasses an urban to rural gradient and a diverse socioeconomic gradient. The watershed lacks a formal institutionalized collaborative watershed management program. To study social connectivity, we studied interorganizational ties or connections created to share information or resources or to spur cooperative management. To study ecological connectivity, we examined the stream bank vegetation and seed dispersal along three 2^nd order streams located in three counties of NJ. Along each stream we sampled four river zones (above a dam, directly below the dam, above a concrete embankment, below a concrete embankment). Once a month at each zone we randomly collected four leaf litter piles, cold stratified for two months, and germinated seeds on sterile soil in the greenhouse. We identified all individuals to species where possible. Vegetation surveys were performed at each zone. We compared plant community structure between litter piles and field vegetation surveys to access movement of seeds along the river.

Results/Conclusions

Preliminary results show non-native invasive plant species such as Artemisia vulgaris and Polygonum cuspidatum promote the greatest connectivity among sites along streams in the Rahway River watershed. These are also the most common herbaceous species on the banks.  Stream banks supporting 153 plant species and 45 species were found in the April 2011 litter collection. Beta-diversity is greatest above dams and least below, suggesting dams homogenize biota downstream, likely by impeding particular species at the dam. Sites above and below concrete embankments have similar biota, indicating these embankments may not filter biota due to the fast-moving currents. The watershed interorganizational network primarily includes municipal governments and is sparse with large gaps. There is a watershed organization with ties to most of the actors, but because of lack of support, this organization has not been able to act as a broker for cooperation across jurisdictions. County governments attempt some coordination along the river system, but collaborative watershed management as a whole does not exist. In order to promote social connectivity and collaborative watershed management of the Rahway River watershed, there is a need for a watershed organization to coordinate the municipality, county, and state governments responsible for managing the river system.