Investigation of the impacts of regulated water levels on biodiversity of Diatoms and Chironomids

Dissertation Abstract – Claire Serieyssol Bleser

In order to determine the timing and magnitude of environmental change resulting from historical water-level manipulation in Voyageurs National Park (VOYA), Minnesota, USA, a before-after, control-impact paleolimnological study in the Rainy Lake drainage begun in 2005. Voyageurs National Park, situated along the Canadian-US border, is largely comprised of the Rainy-Namakan-Kabetogama Lake system. These three lakes were dammed in the early 20th century and have undergone multiple periods of hydromanagement. Lac La Croix, which is situated upstream of VOYA in the Boundary Waters Canoe Area Wilderness and was not impacted by water-level manipulation, was sampled as our control site. A total of five sediment cores was retrieved during the 2005 field season: Kabetogoma Lake; Namakan Lake (Junction Bay); and two cores from Rainy Lake (Grindstone and Kempton Bay); along with a core from our control lake, Lac La Croix. The cores were dated using 210Pb activity to determine sediment age and accumulation rates for the past 150 years. Sediment biogeochemistry was determined using loss-on-ignition analysis. Subfossil diatom communities and chironomids will be analyzed in each core over the last 300-400 years to determine natural (pre-damming and pre-European) variability of biological communities and water quality and their response to European settlement, land-use shifts, damming, and historical water-level management plans. Coupling historical International Joint Commission (IJC) management policy with the sub-fossil record gives an excellent opportunity for determining the effectiveness of a transboundary regulatory agency in managing an international water resource by testing the impact of management decision on biodiversity and improvement/deterioration of water quality.

Dissertation Rationale

Since 1914, when all of the dams were completed, the impacted lakes, which are shared by Minnesota and Ontario, have been manipulated for the benefit of flood control, logging, and hydropower. The lakes fall is under the jurisdiction of the International Joint Commission (IJC) that was formed in 1909 by the Boundary Waters Treaty as a means of preventing and resolving disputes in regards to the use and quality of the boundary waters. Both the U.S.A. and Canada have strong interest in the shared lakes and therefore have relied on the IJC since 1925 to oversee regulation of the lake system. In 1938, the IJC became actively involved in the regulation of Rainy-Namakan-Kabetogama Lake system when it signed the Order Prescribing Method of Regulating the Levels of the Boundary Waters. Thereafter, three different regulations were implemented as a result of severe floods in the region.

However, in 1999, a report compiled by the International Rainy Lake Board of Control (IRLBC) for the IJC recommended that Namakan and Rainy Lakes should have a greater band width (i.e., water level differential) during the summer to allow management to optimize overall habitat conditions that would simulate more “natural” conditions, thereby increasing species diversity or minimizing diversity loss in the system. Based on the recommendations of the IRLBC, the IJC that same year modified the band width regulations with the stipulation that biotic communities and habitats be monitored to determine now they respond to the new regulations. But, many of the biological communities have never been continuously monitored, and very little information is available about the “natural” or pre-damming communities or limnological conditions. The sediment record offers a singular opportunity to examine a continuous record in order to determine the impact of damming, the effect of various band width regulations on biological communities and water quality, and the natural conditions before regulation.

Project significance

In order to sustain or improve our environment for future generations, it is important for society to know how modification of the landscape creates changes to biodiversity and water quality. This project will provide paleolimnologists and paleoecologists with a better understanding of how diatoms and chironomid communities, two widely used paleoecological proxies, respond in lake system water-level manipulations; we will determine how magnitude and frequency of water level manipulations affect biodiversity in a lake system. This, in turn, will provide a better understanding of how to accurately measure the dynamics of diatoms and chironomid communities in regulated lake systems. Agencies and park managers will have a greater understanding of how the lake diatom and chironomid communities can be expected to respond to environmental manipulation.

Furthermore, determining if past management plans have improved or deteriorated the system’s health is critical to future management. In-depth analysis of how certain plans were developed and their respective results will determine flaws and successes. Over the past decade, improvement in our impacted lakes is expected as management plans included not only people’s needs but the system’s health itself. If the system has improved, then the lakes should show signs of better water quality, a more natural fauna and flora, while at the same being able to sustain population needs without resource deterioration. However, if there are no signs of improvement, this research should provide comparable feedback on previous management plans and offer suggestions on improving resource management.

Learning more about the successes and flaws of the IJC is important, because the IJC is one the oldest international water management organization. It could be used as a model for other international watersheds. Therefore, it is important to know its successes and failures, and correct the problems.