The effects of catchment liming on the calcium budget of an acidified Nova Scotia watershed

Abstract

Acidification of South West Nova Scotia’s (SWNS) watersheds from acid rain deposition has led to the depletion of base cations from catchment soils (Clair & Hindar 2005). This has led to a reduction in the acid neutralizing capacity (ANC) of the catchments, acidification of surface waters, and the release of aluminum ions (Ali) into surface waters, which can cause deleterious changes to aquatic ecosystems, and can be particularly harmful to Salmo salar smolts (Clair & Hindar, 2005). There are decreasing trends in calcium concentration in acidified watersheds as calcium is released into streams as a result of ion exchange (Clair, 2004). Catchment liming, the addition of neutralizing compounds such as calcium carbonate (CaCO3), to acidified watersheds has been demonstrated to be an effective mitigation strategy to assist in the recovery of such environments (Clair & Hindar, 2005). The application of 30 tonnes of CaCO3 to an acidified watershed in SWNS in 2012 has been attempted in order to artificially replenish the depleted base cations from the soil and to mitigate the effects of acid rain deposition. This research examined, using a mass balance approach, the calcium budget of an acidified watershed in SWNS. The study addressed the following questions: What were the annual exports and imports of Ca at the Maria Brook catchment, and were they balanced? And did catchment liming change the calcium budget of the Maria Brook catchment in SWNS? Using data from The Canadian Air and Precipitation Monitoring Network (CAPMoN) and from grab samples of the catchment drainage waters, a pre-liming and post-liming calcium budget was constructed. A stage-velocity model was constructed to estimate drainage of water from the system both pre- and post-liming. The nutrient balance was determined from calcium entering the system through precipitation and leaving the system through drainage water (Bormann and Linkens, 1967). It was found that the pre-liming Ca budget was negative, demonstrating that Ca is continually being depleted from the system and that inputs were insufficient to balance exports. The application of 30 tonnes of CaCO3 resulted in increased Ca export from the system and increased stream water Ca concentrations; however these increases only represented a fraction of the Ca added to the system, suggesting that the remainder was taken up by vegetation or was stored in the soil pool. It is recommended that further liming applications be conducted and monitored in order to assess efficacy of catchment liming in remediating the detrimental effects to aquatic communities (Clair et al., 2004) and in replenishing Ca-depleted soils that potentially decrease forest productivity (Yanai, 2005).