Bi-phasic trends in mercury concentrations in blood of Wisconsin common loons during 1992–2010

Abstract

We assessed the ecological risk of mercury (Hg) in aquatic systems by monitoring common loon (Gavia immer) population dynamics and blood Hg concentrations. We report temporal trends in blood Hg concentrations based on 334 samples collected from adults recaptured in subsequent years (resampled 2-9 times) and from 421 blood samples of chicks collected at lakes resampled 2-8 times 1992-2010. Temporal trends were identified with generalized additive mixed effects models and mixed effects models to account for the potential lack of independence among observations from the same loon or same lake. Trend analyses indicated that Hg concentrations in the blood of Wisconsin loons declined over the period 1992-2000, and increased during 2002-2010, but not to the level observed in the early 1990s. The best fitting linear mixed effects model included separate trends for the two time periods. The estimated trend in Hg concentration among the adult loon population during 1992-2000 was -2.6% per year, and the estimated trend during 2002-2010 was +1.8% per year; chick blood Hg concentrations decreased -6.5% per year during 1992-2000, but increased 1.8% per year during 2002-2010. This bi-phasic pattern is similar to trends observed for concentrations of methylmercury and SO(4) in lake water of an intensely studied seepage lake (Little Rock Lake, Vilas County) within our study area. A cause-effect relationship between these independent trends is hypothesized.

Spatial gradients of methylmercury for breeding common loons in the Laurentian Great Lakes region

“…Analysis of samples for total mercury (THg) occurred at several laboratories, and the authors acknowledge the possibility for inter-laboratory error in this study. However, the level of analysis error between laboratories is relatively minor in comparison to the spatial and temporal signal presented here and in companion articles (Monson et al 2011;Meyer et al 2011).…”

“…Yellow perch data were part of a large fish dataset from state, federal, and other sources in the Great Lakes region, developed as part of the Great Lakes Mercury Project (details on this dataset may be found in Monson et al 2011). Loon samples were analyzed as in Evers et al (1998), Evers et al (2003, and Meyer et al (2011). Only data between the years of 1990 and 2009 were included, and only perch data from fish 5-25 cm in length, which are common prey items for loons (Barr 1996).…”

Common Loon Reproductive Success in Canada: the West is Best but Not for Long

“…Methylmercury concentrations are higher (e.g., Evers et al 1998) and pH is lower (e.g., Minns et al 2008) in southeastern than in southwestern Canada, which likely explains why reproductive success in this study was lower in the southeast than in the southwest. Methylmercury is increasing over time in some lakes (e.g., Meyer et al 2011) and pH is remaining stable over time in most lakes in southeastern Canada (Jefferies et al 2003a), which likely explains why reproductive success in this study decreased over time. Methylmercury concentrations are higher (e.g., Bodaly et al 1993) and pH (e.g., Eilers et al 1983) and abundance of forage fish (e.g., Piper et al 2012) are lower in smaller than in larger lakes, which likely explains why reproductive success in this study was lower in smaller than in larger lakes.…”

“…Thus, we predicted that the number of six-week-old young per pair per year would (1) decrease with increasing longitude, i.e., decrease from west-to-east, (2) decrease over time, (3) increase with increasing lake area, and (4) increase with increasing pH (e.g., McNicol et al 1995, Weeber 1999, Timmermans and Jones 2002. We further predicted that longitude × year, year × pH, and lake area × pH interactions would be important (e.g., Alvo 2009, Meyer et al 2011, Piper et al 2012, Weeber 1999. We placed our results in a demographic context by estimating whether reproductive success is sufficient to offset adult and juvenile mortality, i.e., a demographic source, which is identified as a conservation priority for the Common Loon (Evers 2007).…”

“…In addition, methylmercury concentrations are increasing in some locations because of multiple interacting factors that cause methylmercury to increase even though mercury deposition and acid precipitation have declined (Watras and Morrison 2008). For example, methylmercury increased in fish between the mid-1990s and mid-2000s in Wisconsin, Minnesota, and Nova Scotia (Madsen and Stern 2007, Monson 2009, Rasmussen et al 2007, Wyn et al 2010 and mercury increased in Common Loons from 2002 to 2010 in Wisconsin (Meyer et al 2011). Similarly, pH increased in relatively few lakes in eastern Canada during the 1990s, despite concurrent reductions in acid emissions, partly because the acid neutralizing capacity of most lakes remained insufficient to buffer acid inputs (Doka et al 2003, Jefferies et al 2003a.…”