Keji Park: beauty on the rocks (guest blog post)

Communication is an essential part of science. The Canadian Field-Naturalist wants to encourage science communication among Canada's early-career naturalists. Below is a story about a research article in our latest issue, authored by Lauren Banks, a first year Environmental Science graduate student at Trent University. Lauren was not involved in this study.

Kejimkujik (Keji) National Park is shining example of conservation and natural history research in Nova Scotia. Collaborative projects in the park range from working with species at risk like Blanding’s Turtle to providing environmental education to visitors. The intricate river and lake system and surrounding area in Keji is the result of a sustained interaction of biota and geology creating unique networks of ecosystems that have attracted researchers across Canada.

Figure 1 Kejimkujik (Keji) National Park, Nova Scotia. Map created by Jay Fitzsimmons from Google Maps base layer.

Nova Scotia has a diverse geological history dating over a billion years. The Southwest region of the province, where Keji is located, resulted from a geological mish-mash primarily composed of slate, quartzite, and granite bedrock. Unlike softer rocks like limestone, which erodes and releases minerals like calcium carbonate, Keji’s bedrock doesn’t readily erode. With minimal erosion occurring, lakes in the park generally have a low mineral content. Though this is a naturally occurring phenomenon, the lack of minerals in the water can make these lakes susceptible to acidification.

Nova Scotia is often referred to as the ‘tailpipe’ of the eastern seaboard, due to the eastbound wind of the jet stream that can bring air pollutants from central Canada to Nova Scotia. These pollutants can include nitrogen oxides (NOx) and sulphur dioxides (SOx). Once airborne, NOx and SOx can interact with other substances in the atmosphere, resulting in acid rain, acid fog, or even acid snow. Though emission and deposition of these pollutants have declined from their peak deposition in the 1970s and 80s, the effects are still measureable in Keji’s lakes. Due to bedrock geology, these lakes lack a natural ability to buffer the effects of acid rain. This medley of distinctive ecological and geological qualities has created a fascinating setting to ask questions about the environmental effects of acid rain on the most vulnerable types of lakes.

Acid rain biomonitoring

As a part of the Acid Rain Biomonitoring Program, scientists with Environment Canada wanted to know about the impacts of an increasingly acidic environment on invertebrates in Keji’s lakes. In addition, they wanted to establish a baseline of invertebrate diversity and abundance, and assess the potential of using certain species as bioindicators of lake health. Invertebrates play an integral role in the aquatic food web, from filtering algae and assisting with decomposition of plant matter to being a primary food source for fish and waterfowl species. Presence, abundance, and taxa diversity of invertebrates can provide a snapshot of ecosystem structure and function.

This study used different sampling methods to target different types of invertebrates; if you want to survey many types of invertebrates you have to do many types of sampling. In June 2009 and 2010, three sampling methods were used in 20 acidic lakes in and adjacent to Keji. Each of these methods targets different habitats, and together they provided the researchers with a sense of the diversity of invertebrates in these lakes. This aspect of the study is unique, as researchers often focus solely on one species or only use one of these techniques. Zooplankton, generally small free-floating invertebrates, were sampled at the deepest part of the lake using a vertical net haul. The researchers also set minnow traps to get a sense of fish abundance.

Acidic lakes dominated by a few hardy species

Acidity and calcium concentration appeared to be the main drivers of invertebrate abundance and diversity in these lakes. Lakes that had higher calcium and less acidity generally had higher species richness. In acidic lakes fewer taxa were collected, with isopods, beetles, and worms being most abundant. One species of isopod constituted over 30% of the invertebrate populations of 11 of 20 lakes, and seemed to flourish in acidic lakes with low calcium. Two acid-tolerant amphipod species were collected in 55% and 95% of all sampled lakes. Amphipods generally have a shrimp-like appearance and are often called scuds. Snails and clams require calcium to build their shells, and both groups were not found in lakes that were moderately to strongly acidic. Other invertebrates that appeared to be vulnerable to acidic water include leeches, mayflies, and daphnia zooplankton.

Figure 2 - Hyalella azteca, the most abundant amphipod in sampled lakes. Photo by Scott Bauer, courtesy of the US Dept. of Agriculture's Agricultural Research Service.

These results suggest that the invertebrate community is dominated by a few hardy species in acidic lake environments. Having a low number of prey species at the base of the lake food chain can have impacts far beyond the invertebrate communities themselves, since invertebrates are an important food source for many fish and waterfowl.

Lakes vs. rivers for biomonitoring

Invertebrates are often used as bioindicators of pollution in rivers, but their use as bioindicators in lakes is less routine. Invertebrates have proven useful as bioindicators to monitor pollution in rivers and streams. In rivers and streams, the EPT index has been widely applied to monitor changes to these ecosystems. EPT is an acronym for mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera), which are all pollution-sensitive taxa. Though both aquatic ecosystems, lakes and rivers/streams provide vastly different habitats for invertebrates. The EPT index may not be as useful a bioindicator for lakes as for rivers. Understanding invertebrate community dynamics in acid-sensitive lakes is an important step in developing an index to monitor changes to invertebrate communities in lakes.

This study was the first study to perform an inventory of invertebrates in a broad range of lakes at Keji. This baseline can serve as a useful tool for researchers and the public to track changes in the invertebrate community for years to come. However, no invertebrate inventory was completed during the peak of nitrogen oxide and sulphur dioxide deposition, so we may never know the true extent of impacts of acid rain on invertebrates. Continuous environmental and ecological monitoring is essential for understanding the changing environment and our role in environmental degradation and future remediation.

Citation:
Nussbaumer, C., Burgess, N.M., & Weeber, R.C. 2014. Distribution and Abundance of Benthic Macroinvertebrates and Zooplankton in Lakes in Kejimkujik National Park and National Historic Site of Canada, Nova Scotia. The Canadian Field-Naturalist 128(1):1-24. http://www.canadianfieldnaturalist.ca/index.php/cfn/article/view/1545

Lauren Banks is an Environmental Science Master's student at Trent University in Peterborough. She studies freshwater plants, but curiosity has lead her to adventures with bees, martens, and farming.