SURFACE AND GROUND WATER QUALITY IN A RESTORED URBAN STREAM AFFECTED BY ROAD SALTS

In 2001, research began in Minebank Run, an urban stream in Maryland, USA to examine the impact of restoration on water quality. Our research area was to determine if road salts in the surface and ground waters were detrimental to the stream channel restoration. The upstream reach (UP), above the Baltimore I-695 Beltway, was restored in 1998/99, with post-restoration monitoring. The downstream reach (DOWN) was restored in 2004/05 with pre- and post-restoration monitoring. Stream gauges and piezometers were installed in the stream channel and floodplain along multiple transects in both reaches. Statistical analysis identified significant differences in salinity (EC), the road salt related chemistry (Na & Cl), and secondary soil related salt chemistry (Ca, Mg & SO₄) between UP and the greater concentrations in the DOWN surface water. Ground water at the UP and DOWN sites also differed; the DOWN wells all had significantly greater salt concentrations than the corresponding depths in the UP wells

The DOWN ground water salts were significantly greater in the right bank (RB) than the left bank (LB) for Na, Cl, Ca and SO₄ concentrations but Mg concentrations were greater in the LB. During wetter periods (e.g. during road salt application) associated research on the pre-restoration water levels had a toward the stream gradient, but during drought, the RB reversed gradient. The RB cation chemical composition was dominated by Na and was more variable than the Ca dominated LB.

Groundwater quality differed after the restoration. Restoration restructured the DOWN-LB, Na significantly decreased in the wells after restoration but there were significant increasing Na trends. Significant increasing trends also occurred for Cl in these LB wells. Whether the current increasing trends will return to and stabilize at the pre-restoration concentrations is unknown. If the increasing trend in the surface water salinity is indicative, then well water trends are also expected to persist. Salt concentrations are not at levels likely to be detrimental to the stabilizing vegetation. Storm event precipitation induced EC spikes indicated pulsed, elevated salt levels that may affect aquatic biota.

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