Impact of Weather on a Lake Ecosystem, Assessed by Cyclo-Stationary McCa of Long-Term Observations

Abstract

Temperate lake ecosystems are generally characterized by a strong annual cycle, and the relationships between observations of such ecosystems and external forcing variables can exhibit a complex structure. Furthermore, the observational data record is often short. This makes it difficult to assess the relationships between external forcing factors and their impact on the biological succession. Cyclo‐stationary maximum cross‐covariance analysis (MCCA) allows the effects of seasonality to be modeled in a flexible way, and we describe this statistical technique in detail. MCCA offers an objective method to approximate the high‐dimensional total cross‐covariance structure by defining “weighting” patterns. With a predictor set of reduced dimension, a suitable regression between forcing variables and ecological response variables can be set up. Cyclo‐stationary MCCA is used here to analyze the influence of meteorological variables (air temperature, wind speed, global radiation, humidity, and precipitation) on 13 biological and biogeochemical indicator variables of Plußsee, a small lake in northern Germany. The main weather influence on the indicator variables was found to be connected to winter temperature. From the covariance structure the following major signals were detected to be related to higher winter temperature: a more intense spring algal maximum, a higher zooplankton biomass during the algal maximum, a less intense loss of nutrients to the hypolimnion, a higher summer bloom together with changes in the nutrient concentrations, and stronger oxygen consumption in autumn.

The response of freshwater ecosystems to climate variability associated with the North Atlantic Oscillation

“…Adrian, personal communication], so is the timing of the spring bloom, as well as the late winter and early spring phytoplankton biomass in Müggelsee [Weyhenmeyer et al, 1999;Gerten and Adrian, 2000;Straile and Adrian, 2000]. Additionally, reduced ice cover in Plußsee (Germany) following mild winters has been suggested to be responsible for lower transparency in early spring, indicating a higher phytoplankton biomass [Güss et al, 2000].…”

“…An increase in phytoplankton biomass, and probably also primary production, in response to mild winters is likely to result in changes in chemical variables such as pH and the concentrations of O 2 and nutrients. In Plußsee [Güss et al, 2000] and in the Galten Basin of Lake Mälaren [Weyhenmeyer, in prep. ], higher O 2 concentrations as a consequence of increased O 2 production, as well as higher pH and reduced concentrations of SRSi and ammonia resulting from an increased uptake of CO 2 and nutrients, were observed to follow mild winters.…”

“…], higher O 2 concentrations as a consequence of increased O 2 production, as well as higher pH and reduced concentrations of SRSi and ammonia resulting from an increased uptake of CO 2 and nutrients, were observed to follow mild winters. In both lakes, some of these indirect phytoplankton-mediated effects of the NAO last until April and May [Güss et al, 2000;Weyhenmeyer, in prep. ].…”

“…For example, increased epilimnetic O 2 concentrations and increased pH correspond to decreased transparency (indicating a more intense phytoplankton bloom) in Plußsee in July and August [Güss et al, 2000]. In autumn, O 2 concentrations are negatively related to the conditions in the previous winter, indicating an increase in the degradation of particulate organic matter originating from more intense phytoplankton blooms [Güss et al, 2000]. These results suggest that meteorological conditions in winter, and hence also the NAO, play a central role in explaining the chemistry of freshwater systems throughout the year.…”

Climate warming experiments: Design of a mesocosm heating system

“…Most effects of climate change on lake ecosystems have been deduced from models (Byron and Goldman 1990;Regier et al 1990), long-term monitoring (Schindler et al 1990;George and Taylor 1995;Güss et al 2000;Scheffer et al 2001), or paleo-ecological research (Leavitt et al 1997;Vinebrooke et al 1998;Finney et al 2000). Studies of thermal effluents also have advanced our understanding of the potential effects of climate change, but many are confounded by changes in the physical environment, the presence of introduced species or large increases in water temperatures that are inconsistent with current climate change models (Patalas 1970;Klarer and Hickman 1975;Oden 1979;Konopacka and Jesionowska 1995).…”