Dieter Lessmann

Phytoplankton of the extremely acidic mining lakes of Lusatia (Germany) with pH ≤3

Most of the flooded, open-cast lignite mining lakes of Lusatia (Germany) impacted by the oxidation of iron sulphides (pyrite and marcasite) are extremely acidic. Of 32 lakes regularly studied from 1995 to 1998, 14 have a pH <3 (median pH 2.3–2.9). These lakes are typically buffered by high concentrations of Fe (III) and have high conductivity (1000–5000 μS cm−1). Concentrations of dissolved inorganic carbon (DIC) and phosphorus are typically extremely low. These factors result in a very different environment for algae than found in neutral and acid-rain impacted lakes. The planktonic algal flora is generally dominated by flagellates belonging to genera of Chlorophyta (Chlamydomonas), Heterokontophyta of the class Chrysophyceae (Ochromonas, Chromulina), Cryptophyta (Cyathomonas) and Euglenophyta (Lepocinclis, Euglena mutabilis). Near-spherical non-motile Chlorophyta (Nanochlorum sp.), Heterokontophyta of the class Bacillariophyceae (Eunotia exigua, Nitzschia), Dinophyta (Gymnodinium, Peridinium umbonatum), other Chlorophyta (Scourfieldia cordiformis) and Cryptophyta (Rhodomonas minuta) are also found.

Lake Plessa 107 (Lusatia, Germany) — an extremely acidic shallow mining lake

Lake Plessa 107 is an example of the older, relatively small and often shallow mining lakes of Lusatia which only have groundwater inflow. From a morphological point of view, the lake should be polymictic with short stratified periods. But besides temperature, mixing is also determined by chemical gradients in the water column that can lead up to monomixis. The lake water shows an extreme acidification with high concentrations of calcium, iron, aluminium, manganese and sulphate. Despite low TIC and TP concentrations allowing only a low primary production in the pelagial within the oligotrophic range, anoxic conditions can occur during stratification because of Fe(II) oxidation and anoxic groundwater inflow. The phytoplankton is dominated by phytoflagellates. Chlorophyll concentrations follow a yearly pattern determined by temperature and light availability. The zooplankton consists of two rotifer species, ciliates and heliozoans. Sediment analyses show contrary depth gradients of Fe and P with a very high fraction of Fe in the upper sediment layers (up to 60% of DW) which decreases with depth. Probably due to groundwater inflow, at some sites substantial decreases in redox potential and conductivity can be observed with increasing sediment depth accompanied by increases of pH, DOC, DIC and DIP concentrations. No correlations have been found between the available phosphorus or carbon concentrations in the sediment porewater and the phytobenthic biomass. Euglena mutabilis (Euglenophyceae) and Pinnularia acoricola (Bacillariophyceae) are the dominant phytobenthic species. Lake Plessa 107 has a benthic food-web that consists of benthic algae, chironomids and corixids and a pelagic food-web which is composed of phytoflagellates, rotifers, ciliates and heliozoans. The two food-webs are not coupled because larger prey organisms such as crustaceans are missing.

Aspects of phytoplankton succession and spatial distribution in an acidic mining lake (Plessa 117, Germany)

In Germany, several hundred mining lakes have been formed in the last century. The majority of these water bodies is strongly influenced by high concentrations of dissolved ions and high acidity, and shows pH values around 3. Hereby, a first evaluation is given on the relevance of different parameters, regulating the phytoplankton composition and seasonal succession in the extremely acidic Lake Grunewalde, Lusatia. The phytoplankton biocoenosis, which was analysed for the period April 1996–July 2001, was of low biodiversity with a dominance of the phytoflagellates Ochromonas (Chrysophyceae), Chlamydomonas (Chlorophyta) and Gymnodinium (Dinophyceae). The development of the phytoplankton biomass was low with an average biovolume of 0.64 mm3 l–1. The phytoplankton succession revealed a clear dependence from the inorganic carbon, which is, in combination with phosphorus, the limiting major nutrient in acidic lakes. Higher TIC concentrations occurred during ice covering and stagnation periods in the hypolimnion, and were responsible for rapid increases of the planktonic populations with a maximum biovolume around 2–3 mm3 l–1. Vertical gradients of hydrochemical parameters and plankton distribution were assessed during the summer stratification period. A daily migration pattern was shown for the dominant mixotrophic nanoflagellate Ochromonas, living in deeper layers of the epi- and metalimnion and migrating to the lake surface during lowering light conditions in the evening. This behaviour is explained as a strategy to receive optimal light supply and to overcome nutrient stress in periods of strong physico-chemical gradients.

Estimation of lake water—groundwater interactions in meromictic mining lakes by modelling isotope signatures of lake water

Abstract A method is presented to assess lake water–groundwater interactions by modelling isotope signatures of lake water using meteorological parameters and field data. The modelling of δ18O and δD variations offers information about the groundwater influx into a meromictic Lusatian mining lake. Therefore, a water balance model is combined with an isotope water balance model to estimate analogies between simulated and measured isotope signatures within the lake water body. The model is operated with different evaporation rates to predict δ18O and δD values in a lake that is only controlled by weather conditions with neither groundwater inflow nor outflow. Comparisons between modelled and measured isotope values show whether the lake is fed by the groundwater or not. Furthermore, our investigations show that an adaptation of the Craig and Gordon model [H. Craig, L.I. Gordon. Deuterium and oxygen-18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperature, Spoleto, E. Tongiorgi (Ed.), pp. 9–130, Consiglio Nazionale delle Ricerche, Laboratorio di Geologia Nucleare, Pisa (1965).] to specific conditions in temperate regions seems necessary.

Acidification control of phytoplankton diversity, spatial distribution and trophy in mining lakes

The abandoning of a multitude of opencast lignite mines in eastern Germany since 1990 is leaving large residual holes of several km in which new lakes form. During recent years, these lakes have become a major field of applied limnology in the course of the development of a multi-functional posr-mining landscape (NIXDORF et al. 1997, GELLER et al. 1998). The main problem with the redevelopment of many mining lakes is their severe acidification caused by pyrite oxidarion. In the overburden dumps, pyrite is oxidized in the presence of oxygen and water by chemical and bacteria-caralyzed processes releasing hydrogen ions (EVANGELOU 1994). The acidification has major consequences for the biocoenoses of the mining lakes. Some effects of the extreme hydrochemistry on phytoplankton biocoenoses are analyzed with regard ro differences in diversiry, spatial distribution and trophy of five lakes in Lusatia (Brandenburg and Saxony, Germany).

Hydrogeochemistry of groundwater seepage into an acidic mining lake

In the Lusatian Lignite Mining District 259 mining lakes (ML) originate from abandoned mines. They significantly differ in their morphometry and most are strongly acidic (HEMM et al. 2002). The oxidation of sedimentary pyrite in aerated dump sediments (tertiary sands) forms acid mine drainage rich in iron and sulphate, which has decisive influence on matter flux, biocoenotic development and possible water uses (e.g. for recreation or municipal water supply; UHLMANN et al. 2001). Hydrological processes in mining lakes are dominated by groundwater (HOFMANN et al. 2004). During the last three decades seepage meters were mainly installed in shelf regions o f oceans, estuaries or 1akes to quantify groundwater flux (LEE 1977, BOYLE 1994, BuRNETT et al. 2002), but only in a few acid-mining 1akes the ground water flux has been measured using this technique (80ZAU et al. 2000, WEBER 2000). The main purpose of this study was to investigate the interaction of acid mine drainage with the sediment by using seepage meters. Therefore, ML Plessa 117 was chosen as a typical example ofmining lakes in areas devastated by geo1ogical, hydrogeologica1 and hydrological changes.

Meromixis in mining lake Waldsee, Germany: hydrological and geochemical aspects of stratification

Since meromixis was first described by FrNDENEGG (1932), several natural meromictic lakes have been described (HoNGVE 2002, HAKALA et al. 2004). Meromixis can also be a common feature in mining lakes. A certain morphometry (high depth, small surface area) and the inflow of highly mineralised groundwater promote the formation of permanent density stratification. A well-known example for artificial meromixis is the Island Copper Mine (Vancouver Island, BC/Canada; FrsHER & LAWRENCE 2000). In the Lusatian mining district, where lignite mining has lasted for more than 200 years, several meromictic mining lakes are known. Some have shown a permanent density stratification, such as Lake Lugteich (NrxDORF et al. 2001); others for a certain period, such as Lake Plessa ll1 (KARAKAS et al. 2003). The meromixis ofthe Lusatian mining lakes originates mainly from interna! geochemical and biological reactions with the transformation of iron as the predominant process (BoEHRER & ScHULTZE 2005). We studied the influence of groundwater inflow and internai geochemical processes that contribute to the development of meromixis in a small meromictic lake of the Lusatian mining district.

Effects of winter temperature on phytoplankton development in acidic mining lakes

Mining lakes are within the focus oflirnnological and public interest in many countries because they have unusal mineral content and can comprise a great portion of standing waters in certain areas. Due to pyrite oxidation, many mining lakes are extremely acidic and therefore differ considerably from natural circumneutral lakes in their chemical and biological characteristics (GELLER et al. 1998, LESSMANN & NIXDORF 2000). In central Europe deep lakes are usually regarded as dimictic. A presupposition for stable winter stagnation is the formation of ice cover, which depends on the duration of the frost period. Within the last ten years central Europe has seen several mild winters that inhibited the formation of a long-lasting ice cover and thus the occurrence of a stable winter stagnation. The importance of occurrence and duration of winter ice cover and winter stagnation for the phytoplankton development is shown by the example of Mining Lake (ML) Piessa 117 of the Lusatian lignite mining district (Germany). This study compares the relatively mild winter 2001/2003 with the strong winter 2002/2003 and analyzes phytoplankton development in winters of 1997 to 2000.