Historical Changes in Connecticut Lakes Over a 55‐Year Period

Abstract

Changes in the chemical and physical conditions of 42 Connecticut lakes are compared between three time periods, the late 1930s, the mid-to late 1970s and the early 199Os. On average, lakes have decreased in Secchi disk depth by 1.2 m and doubled in total phosphorus concentration, many in a unidirectional manner. As a result, the suite of lakes can be characterized as having shifted from an oligo-mesotrophic condition (1930s) to a late mesotrophic condition (19908). Since the 19708, lakes have increased in base cation concentrations an average of 70 peq/L, many as the result of an increase in sodium. Increases in sodium were generally coupled with increases in chloride ions. Many of the lakes positioned in watersheds that have become more residential since the 19308 and/or 19708 have also increased in alkalinity. Despite the overall increase in base cations, chloride, and alkalinity, about 25% of the waterbodies that have remained situated in primarily forested watersheds in crystalline rock regions have decreased in total cation concentrations; about half of these lakes have also significantly decreased in alkalinity since the 1930s. The changes are discussed in relation to the degree of urbanization of the watersheds over the same time period.

Increased salinization of fresh water in the northeastern United States

“…Our observations of long-term increases in chloride concentrations in northern rural areas and in rapidly developing areas located in relatively warm climates, such as Maryland, suggest that chloride pollution may be pervasive across seasons and large geographic areas of the northeastern United States. Over time, a gradual accumulation of chloride in groundwater can lead to elevated concentrations during baseflow conditions in the summer months and can contribute to long-term increases in the baseline salinity of surface waters (3,5,15). Related work has shown increasing salinity in the lakes of the midwestern United States due to road salt (16,17).…”

“…Our observations suggest that even small changes in land use have resulted in large changes in the baseline salinity of aquatic systems. Moreover, the accumulation of road salt in aquifers and groundwater has eventually led to increased salinity throughout all seasons and across years in the northeastern United States and may persist for decades, even if use of salt is discontinued (14,5). Given that land-use change is rapid in many regions of the world (9,11,14,(30)(31)(32), we suggest that salinization associated with increasing suburban and urbanization deserves attention as one of the most significant threats to the integrity of freshwater ecosystems in the northeastern United States.…”

“…Long-term salinization of surface waters associated with increasing coverage by roadways and suburban and urban development has been less considered, although previous research has documented sharp increases in concentrations of sodium and chloride in aquatic systems of the rural northeastern United States over decades due to the use of road salt (2)(3)(4)(5). Our analysis shows that baseline salinity is now increasing at a regional scale in the northeastern United States toward thresholds beyond which significant changes in ecological communities and ecosystem functions can be expected.…”

From icy roads to salty streams

“…These problems include toxicity to plants and fish, groundwater contamination, and human health interactions, particularly salt intake and hypertension (7)(8)(9). In consequence, researchers have been monitoring increased salt concentrations in streams and groundwater for decades (4)(5)(6)10).…”

Seasonality and trends in the Secchi disk transparency of Lake Ladoga

“…Secchi disk transparency is the most frequently measured characteristic of lake waters and can be regarded as a parameter for analyzing interannual (climatic) changes in the lake. For example, climatic trends in Secchi disk transparency have been detected in various North American lakes (Francis et al, 1994;Siver et al, 1996;Lathrop et al, 1999).…”