The fish that revealed changes around old millponds

Old industrial water, new comparisons

Many Pinelands lakes began as impoundments for sawmills, ironmaking, paper production or cranberry growing. Commission researchers selected thirty such water bodies along a gradient of upstream development and upland agriculture. They divided the drainage basins into five groups, from less than ten percent altered land to forty percent or more. Commission, Impoundment Study.

This design compared human-made lakes with different watershed conditions rather than treating every dammed pond as equally degraded. The project examined water chemistry alongside diatoms, plants, fish, frogs and toads. Its question was whether biological changes appeared at particular levels of surrounding alteration. Commission, Impoundment Study.

What the water measurements showed

The investigators took pH and conductivity measurements through the growing seasons of 2003–2005, then collected additional water-quality samples at twenty-four lakes in 2006. The least-altered group had a median pH of 4.4, compared with 6.6 in the most-altered group; median specific conductance rose from 51.8 to 104.4 microsiemens per centimeter. These are group summaries from the thirty-lake comparison, not a before-and-after record for any one pond. Final report, Table 1 and methods.

More species was not necessarily the same community

The 2007 report records twenty fish species, grouped as restricted, widespread or nonnative. Of 8,300 individual fish collected, 2,588 could be identified only to genus and were excluded from the species analysis. That explicit exclusion is important: the catch total and the data used to compare species were different quantities. Zampella and colleagues, final impoundment report (2007).

Impoundments in the least-altered group had a lower percentage of nonnative species and a higher percentage of restricted species than those in the most-altered group. Nonnative species richness also differed between those ends of the gradient. The report classifies mud sunfish, blackbanded sunfish and swamp darter among species restricted to the regional Pinelands fauna. Across the sampled lakes, overall species richness correlated positively with altered land, while the share of restricted fish correlated negatively and the share of nonnative fish positively. Only nonnative-species richness differed significantly across the five land-use groups in the group comparison. A longer fish list could therefore describe a changed community rather than a healthier one. Final report, Tables 11–12 and fish results.