Increase In Water Colour Research Articles

Pike Mercury Concentration in Small Boreal Headwater Lakes During Four Decades of Regional and Local Changes

We measured the total mercury (THg) concentration in the muscle of northern pike (Esox lucius L.) from 12 boreal headwater lakes once per decade during the 1980s to 2010s. Relations of pike THg to regional environmental changes, such as reduction of acid deposition and increase in water colour (i.e. browning), were examined as well as the effects of local lake-specific changes caused by introduced beavers (Castor canadensis) and intensive fishing of pike. No consistent decrease in pike THg took place during 1983–2013 despite the reductions in mercury emissions from European sources since the 1990s and the associated decreased mercury deposition in Finland. In most of the lakes, individual pike exceeded the recommended limit for human consumption (1 mg kg−1, wet weight). The highest THg levels were recorded in 2002 following intensive browning of the lakes in the 1990s in connection with decreased sulphate deposition. The effects of acid deposition were only seen as the highest pike THg in the two most acidic lakes in the early 1980s. After taking length effects into account, pike THg had a negative relationship with growth (i.e. growth dilution), but a positive relationship with water colour, iron, nutrients and maximum lake depth. Females grew faster and had lower THg than males. Pike THg was elevated in beaver-impacted lakes. Experimental removal of pike from three study lakes during 2005–2013 resulted in a decrease of pike THg. These findings emphasize the significance of local abiotic and biotic drivers when interpreting the regional long-term trends in pike THg.

Responses of a Submerged Macrophyte Potamogeton crispus and Epiphytic Biofilm to Humic-Substance Enrichment Coupled with Brownification in Freshwater Habitats

Brownification denotes increasing water color, partly caused by increasing dissolved organic matter of terrestrial origin in freshwater. Brownification has become a wide-spread environmental problem because water color alters the physicochemical environment and biological communities in aquatic ecosystems. However, our understanding of its ecological effects on aquatic macrophytes is limited. Here, an indoor mesocosm experiment with a common submerged macrophyte, Potamogeton crispus, along an increasing gradient of brownification was conducted over a period of 42 days. Results showed that P. crispus was able to overcome low degrees of brownification owing to the plasticity in morphological and physiological traits and P. crispus growth even benefitted from the concomitant nutrients along with brownification. However, the macrophyte growth was negatively affected by a 10-fold increase in water color beyond its current level. Additionally, collapse in antioxidant systems and potent photosynthesis inhibition implied that P. crispus could not adapt to the low-light stress generated under the high degree of brownification. Epiphytic bacteria are more sensitive to brownification than their hosts. Any degree of brownification initially caused a decrease in microbial diversity of epiphytic biofilm, whereafter the concomitant nutrients under brownification favored the growth of epiphytic microorganisms. The shading effect of a large number of epiphytic biofilms under brownification may further aggravate the low-light stress on macrophytes. Overall, the study provides new insights into the comprehensive effects and underlying mechanisms of brownification on macrophytes.

Evaluation of treatment performance for one constructed wetland in a Swedish forest – A case study with emphasis on brownification mitigation

Brownification refers to the increase in water colour reported in many freshwater systems. Constructed wetlands (CW) are commonly used for pollutant mitigation, including the causes of brownification. This study aimed to investigate the effects of a CW established in a forest area with high colour and low pH on its capability to reduce nutrient and colour. The inflow and outflow colour (mg Pt/L), total organic carbon (TOC), and iron (Fe) were assessed daily over a period of recorded dynamic flows during spring and autumn 2019 (15 and 19 days, respectively). Total nitrogen (Ntot) and phosphorus (Ptot) were also assessed to verify the removal efficiency of this mature constructed wetland. The prevailing hydraulic retention time (HRT) was assessed using conservative tracing. The results showed that the colour, TOC, and Fe were not reduced during the evaluation period. In contrast, while colour did not change (4–8% increase) over the assessed periods, TOC and iron significantly increased by 7.7% and 29.5%, respectively, during spring (4.2% and 10.6% during autumn). As Ntot and Ptot increased by 14.8% and 120%, respectively, during spring (7.4% and 8.8% during autumn), we concluded that constructed wetlands designed for nutrient control offer little potential for the mitigation of brownification, as expressed by colour, under low pH conditions.

Состояние экосистемы озера Хедо (западная Карелия) в условиях рыбоводной деятельности

The article highlights the analyzes of the ecosystem of Lake Khedo (Republic of Karelia) under conditions of growing anthropogenic load caused by using the lake for breeding trout in fish cages based on the proper and literature data. Comparative analysis of hydrochemical data before the operation of the farm (until 2005) and after showed a twofold increase in water color (70-150°), which indicates an increased content of organic pollutants (humus, peat, silt). Also in the reservoir there are increased nitrogen and phosphorus compounds. Previously, the concentration of total phosphorus did not exceed 0.01 mg/l, today it reaches 0.02 mg/l. The main factor contributing to the satisfactory state of Lake Khedo is the high water flow rate, due to which most biogens are flown outside the lake. The data on the main hydrobiological indicators of the lake (phytozooplankton and zoobenthos) are presented. It has been stated that if earlier the reservoir corresponded to the mesohumous oligotrophic type, at present it reaches the initial level of mesotrophy, which is probably facilitated by the long-term cage cultivation of the aquaculture object. In terms of the abundance of organisms of the initial trophic levels, the reservoir corresponds to α-mesotrophic type. The lake is inhabited by 8 species of fish, and the valuable ones include whitefish Coregonus lavaretus (L.) and vendace Coregonus albula (L.). The results of the research made it possible to clarify the total production of commercial trout, which amounted to 300 tons per year and doesn’t exceed the total biogenic load. Recommendations on timing the regular ecological expertise of the lake and the adjustment of production volumes are given

Does Water Brownification Affect Duckweeds in Freshwaters? Results from a Laboratory Experiment

The influence of water brownification (an increase in water color) on floating-leaved macrophytes appears to be an important issue in predicting the consequences of climate change in freshwater ecosystems. To fill the gap in the knowledge in this area, we performed a laboratory experiment aiming to test the impact of humic acid (HA) on Lemna minor sampled from an oxbow lake. Plants were exposed over seven days to four different additions of pure HA (resulting in DOC concentrations between 5.0 ± 0.1 mg dm−3 and 36.5 ± 0.4 mg dm−3). Changes in duckweed total fresh biomass, leaf area and the root length were measured, as well as the concentrations of total phosphorus, phosphates and nitrates in the water. The study did not find any significant decrease in either the biomass or leaf area of L. minor under conditions of enhanced HA content. However, we found that a moderate increase in HA in water promoted the growth of duckweed roots, thus, increasing the biomass but not the leaf area. In contrast, a large increase in HA in the water suppressed the growth of roots in L. minor, which was also in coincidence with less nutrient depletion in the water.

What is the extent of water brownification in Lake Onego, Russia?

In the past 26 years the transport of allochthonous matter into Lake Onego has increased. Water brownification in Petrozavodsk Bay, a northwestern bay in Lake Onego, and in the Shuya River, a tributary of the bay, was shown earlier to begin in spring. The goal of this paper was to find out whether brownification spreads from Petrozavodsk Bay to the central part of the lake in summer. Spearman’s correlation coefficient and linear correlation coefficient confirm a significant (p < 0.05) increase in water color in Petrozavodsk Bay in the summers of 1992–2018. A tendency for increasing water color was found in the Central Onego’s epilimnion. Total iron and CO2 concentrations in the epilimnion have increased and pH values have decreased both in Petrozavodsk Bay and in the Central Onego. In the Central Onego’s hypolimnion, only total iron and CO2 concentrations have considerably increased. However, the present lake ecosystem is resistant to the increased effect of allochthonous matter due to long water renewal time and self-purification. In spite of a significant increase in CO2 concentration in the lake water, the bicarbonate buffer system maintains the acid-base equilibrium and the changes revealed are not considered critical for the ecosystem.

Water transparency affects the survival of the medusa stage of the invasive freshwater jellyfish Craspedacusta sowerbii

Craspedacusta sowerbii is a global invader of inland waters, but little is known on what environmental factors control its colonization success. We hypothesized that water transparency and thus, exposure to UV radiation are relevant for the colonization success of this relatively transparent invasive hydroid. Here we used field and laboratory experiments to assess the effect of natural solar radiation and artificial UV radiation on the medusa stage of C. sowerbii across natural and simulated water transparency gradients in three Chilean Patagonian lakes. Short-term exposure of the jellyfish to artificial UV radiation under low Dissolved Organic Carbon (DOC) treatments induced mortality and caused sublethal effects such as swimming anomalies and production of reactive oxygen species. Outdoor exposure of jellyfish to full solar radiation in the most transparent water (Lake Ranco; DOC = 0.6 mg l−1) resulted in almost complete mortality. However, higher DOC contents provided partial or almost complete protection against the adverse impact of UV radiation. Overall, our findings provide evidence of the role of underwater light conditions in the underlying mechanisms that may favor the invasion of this gelatinous alien species in inland waters. The results imply that under the current “brownification” of lakes, an increase in water color might provide more favorable conditions for the invasion process of this hydroid.

Spatial Variation in Nutrient and Water Color Effects on Lake Chlorophyll at Macroscales.

The nutrient-water color paradigm is a framework to characterize lake trophic status by relating lake primary productivity to both nutrients and water color, the colored component of dissolved organic carbon. Total phosphorus (TP), a limiting nutrient, and water color, a strong light attenuator, influence lake chlorophyll a concentrations (CHL). But, these relationships have been shown in previous studies to be highly variable, which may be related to differences in lake and catchment geomorphology, the forms of nutrients and carbon entering the system, and lake community composition. Because many of these factors vary across space it is likely that lake nutrient and water color relationships with CHL exhibit spatial autocorrelation, such that lakes near one another have similar relationships compared to lakes further away. Including this spatial dependency in models may improve CHL predictions and clarify how well the nutrient-water color paradigm applies to lakes distributed across diverse landscape settings. However, few studies have explicitly examined spatial heterogeneity in the effects of TP and water color together on lake CHL. In this study, we examined spatial variation in TP and water color relationships with CHL in over 800 north temperate lakes using spatially-varying coefficient models (SVC), a robust statistical method that applies a Bayesian framework to explore space-varying and scale-dependent relationships. We found that TP and water color relationships were spatially autocorrelated and that allowing for these relationships to vary by individual lakes over space improved the model fit and predictive performance as compared to models that did not vary over space. The magnitudes of TP effects on CHL differed across lakes such that a 1 μg/L increase in TP resulted in increased CHL ranging from 2–24 μg/L across lake locations. Water color was not related to CHL for the majority of lakes, but there were some locations where water color had a positive effect such that a unit increase in water color resulted in a 2 μg/L increase in CHL and other locations where it had a negative effect such that a unit increase in water color resulted in a 2 μg/L decrease in CHL. In addition, the spatial scales that captured variation in TP and water color effects were different for our study lakes. Variation in TP–CHL relationships was observed at intermediate distances (~20 km) compared to variation in water color–CHL relationships that was observed at regional distances (~200 km). These results demonstrate that there are lake-to-lake differences in the effects of TP and water color on lake CHL and that this variation is spatially structured. Quantifying spatial structure in these relationships furthers our understanding of the variability in these relationships at macroscales and would improve model prediction of chlorophyll a to better meet lake management goals.

The effect of lake browning and respiration mode on the burial and fate of carbon and mercury in the sediment of two boreal lakes

AbstractIn many northern temperate regions, the water color of lakes has increased over the past decades (“lake browning”), probably caused by an increased export of dissolved organic matter from soils. We investigated if the increase in water color in two lakes in Norway has resulted in increased burial of organic carbon (OC) and mercury (Hg) in the sediments and if the Hg was prone to methylation. Lake Solbergvann experienced a threefold water color increase, and OC burial increased approximately twofold concomitant to the water color increase. This lake had prolonged periods of anoxic bottom water, and anoxic OC mineralization rates were only about half of the oxic OC mineralization rates (7.7 and 17.5 g C m−2 yr−1, respectively), contributing to an efficient OC burial. In Lake Elvåga, where water color increase was only approximately twofold and bottom water was oxygenated, no recent increase in OC burial could be observed. Hg burial increased strongly in both lakes (threefold and 1.6‐fold in Lake Solbergvann and Lake Elvåga, respectively), again concomitant to the recent water color increase. The proportion of methylated Hg (MeHg) in surficial sediment was 1 order of magnitude higher in Lake Elvåga (up to 6% MeHg) than in Lake Solbergvann (0.2–0.6% MeHg), probably related to the different oxygenation regimes. We conclude that lake browning can result in increased OC and Hg burial in lake sediments, but the extent of browning and the dominating mode of sediment respiration (aerobic or anaerobic) strongly affect burial and fate of OC and Hg in sediments.

Consequences for pelagic energy mobilisation of a sudden browning episode without a clear increase in DOC concentration: a case of a boreal pristine lake

In the boreal zone, episodes of heavy rains are among the most conspicuous events disturbing aquatic ecosystems. Due to climate change they are predicted to become more frequent and intense, leading on browning of lakes. We assessed the possible effects of heavy rains to DOC concentration and water colour and resulting impacts on functioning of a headwater lake with naturally high water colour and concentration of allochthonous DOC. The weekly measurements were carried out in summers 2002–2004; the first 2 years had normal and the last year very high summer precipitation. The rains resulted in rapid increase in water colour, but not in DOC. We hypothesised that due to browning, irrespective of whether it stems from an increase in brownish DOC or other coloured substances, photosynthesis decreases, bacterial activity increases, and the lake becomes more heterotrophic. We also anticipated that due to strengthened heterotrophy, the period with apparent net autotrophy and CO2 flux onto the lake would disappear. To test our hypothesis, we measured autotrophic inorganic carbon uptake of photosynthetic organisms as well as dark fixation of inorganic carbon, community respiration and leucine uptake. Finally, we compared the results to CO2 flux measurements with an eddy covariance technique. Our hypotheses were only partly supported since there were no drastic changes in any of the metabolic processes measured. Although the lake ecosystem became slightly more heterotrophic, primary production was still occasionally higher than community respiration and the lake could act as a sink of CO2. Thus regarding metabolic processes, the ecosystem of this pristine lake was not strongly disturbed by the sudden browning episode.

Warming and browning of lakes: consequences for pelagic carbon metabolism and sediment delivery

Summary Thousands of lakes in the Northern Hemisphere are experiencing a continuous increase in water temperature and colour. While increasing temperature is an effect of climate change, several factors are suggested to drive the increasing water colour, including climate change, altered land use and reversed acidification. In this mesocosm study, we study the effects on pelagic production and sedimentation of organic carbon from a 3 °C increase in temperature, a doubling of water colour and a combination of increased temperature and water colour. These manipulations correspond to the predicted development in water colour and temperature in northern temperate systems within the life time of the next generation. The water and plankton communities in the mesocosms were taken from an oligohumic and mesotrophic lake, and the increase in water colour was achieved by the additions of water from a humic lake. The experiment ran from early March to late October. In accordance with our predictions and previous cross‐system analyses, net carbon production (NCP) and organic carbon sedimentation decreased in response to increasing water colour. At odds with current theory, NCP and sedimentation increased in heated treatments, as not only respiration but also gross production increased in response to temperature. There were no synergistic effects between warming and browning. These results imply that warming may enhance pelagic delivery of organic carbon to sediments. This could potentially offset a reduction in burial efficiency of organic carbon, which has been projected based on a positive relationship between carbon mineralisation in sediments and temperature.

Long-term changes in phytoplankton in a humic lake in response to the water level rising: the effects of beaver engineering on a freshwater ecosystem

Although water level changes are supposed to be a key factor affecting the functioning of lake ecosystems, knowledge on this topic is scarce, particularly for humic lakes. This paper presents the results of 18 years’ research on a small humic lake exposed to hydrological change (rising of the water level), which was induced by spontaneous colonization of the lake by the European beaver (Castor fiber L.). We put forward a hypothesis that this change will be reflected in the quantity and structure of summer phytoplankton due to expected changes in the water chemistry. We noted a statistically significant decrease in total phosphorus and calcium concentrations, electrolytic conductivity, and Secchi disc transparency, and an increase in water color. The phytoplankton structure changed, with cyanoprocaryota and greens decreasing and flagellates increasing. The alteration was observed in a lake which had previously been drained by ditches, so beaver damming appeared to cause the return of the lake to its original endorheic conditions as well as to a water chemistry and phytoplankton structure more typical of undisturbed humic lakes.

The effect of drain blocking on the dissolved organic carbon (DOC) budget of an upland peat catchment in the UK

Summary Extensive drainage of UK peatlands has been associated with dehydration of the peat, an increase in water colour and a loss of carbon storage. It has been considered that the blocking of these drainage channels represents a means of peat restoration and a way of reducing dissolved organic carbon (DOC) losses to surface waters. This study aimed to assess the effectiveness of drain blocking at both an individual drain scale and at a larger catchment scale (up to 1 km 2 ). A series of blocked and unblocked catchments were studied in Upper Teesdale, Northern England. A detailed sampling programme was undertaken in which a series of drains were studied in the 12 months prior to and post blocking in comparison to a set of drains that were left unblocked and a catchment of similar scale where there had never been drainage. These stream networks were monitored for both their DOC concentration and export (flux per unit area). The results show that: (i) For DOC concentrations, a significant decline due to drain-blocking was only found at the first order scale when considered relative to control and relative to a pre-blocking period; (ii) drain blocking significantly reduces DOC export by reducing water yield in the drain and that the size of this DOC export reduction declines with increasing scale from 9.2% on zero order drains to 2.2% on first order drains; (iii) a linear relationship exists between DOC export and water yield at the zero order scale but this relationship becomes more complex at the first order scale as the relationship takes on the characteristics of a mixing model reflecting the effect of changing water sources with scale and providing evidence of the existence of flow bypassing drain blocks. The results suggest that effects of drain blocking decrease with increasing scale and that the presence of bypass flow around zero order blockages may limit the success of drain blocking as a method of reducing DOC loss as scale increases.

Increasing iron concentrations in surface waters – a factor behind brownification?

Abstract. Browning of inland waters has been noted over large parts of the Northern hemisphere and is a phenomenon with both ecological and societal consequences. The increase in water color is generally ascribed to increasing concentrations of dissolved organic matter of terrestrial origin. However, oftentimes the increase in water color is larger than that of organic matter, implying that changes in the concentration of organic matter alone cannot explain the enhanced water color. Water color is known to be affected also by the quality of organic matter and the prevalence of iron. Here we investigated trends in water color, organic matter and iron between 1972 and 2010 in 30 rivers draining into the Swedish coast (data from the national Swedish monitoring program), and performed a laboratory iron addition experiment to natural waters, to evaluate the role of iron and organic matter in determining water color. By comparing the effect of iron additions on water color in the experiment, to variation in water color and iron concentration in the monitoring data, we show that iron can explain a significant share of the variation in water color (on average 25 %), especially in the rivers in the north of Sweden (up to 74 %). Furthermore, positive trends for iron are seen in 27 of 30 rivers (21–468 %) and the increase in iron is larger than that of organic matter, indicating that iron and organic matter concentrations are controlled by similar but not identical processes. We speculate that increasing iron concentrations can be caused by changes in redox conditions, that mean that more anoxic water with high concentrations of soluble FeII are feeding into the surface waters. More studies are needed about why iron is increasing so strongly, since both causes and consequences are partly different from those of increasing organic matter content.

Changes in water colour between 1986 and 2006 in the headwaters of the River Nidd, Yorkshire, UK

This study compares the spatial and temporal variability of water colour for fifteen sub-catchments of the River Nidd, northeast England, in 1986 and 2006/2007. Between 1986 and 2006/2007, mean annual water colour increased in all the sub-catchments. However, there was considerable variation in the increase, which ranged from 22 to 155%. Statistical analysis revealed that the sub-catchments could be split into two ‘types’ based on water chemistry and therefore dominant source of runoff; type 1 where flow was dominated by runoff from peat and type 2 where a greater contribution of flow appears to originate from mineral soil horizons, as indicated by the higher silicon, base cation concentrations and pH values. Largest proportional increases in water colour were observed in the sub-catchments that had the smaller mean annual water colour values in 1986 which were, in general, the type 2 sub-catchments. The higher rate of water colour increase in the type 2 catchments, in comparison to the type 1 catchments, may be related to changes in adsorption of dissolved organic carbon (DOC) within the mineral horizons of the organo-mineral soils on the lower catchment slopes possibly as a result of changes in acid sulphur deposition.

Increased colour and organic acid concentrations in Norwegian forest lakes and drinking water ? a result of increased precipitation?

Recently there have been major increases in water colour and dissolved organic carbon (DOC) in many forest lakes that serve as drinking water reservoirs in the southern part of Norway. We studied changes in the physical and chemical properties in (I) a selected group of lakes and (II) raw water from the municipal waterworks of Oslo since 1983 and 1976, respectively. The largest increase in DOC and water colour occurred between 1997 and 2001. Statistically significant correlations are seen between water colour and accumulated amounts of precipitation, while variation in temperature had no apparent effect. Despite significant reduction in sulphate concentrations in precipitation and lake waters since 1980, the lakes were more acidic in 2000 and 2001 than in previous years. Increases in colour and acidity, together with somewhat minor changes in DOC concentrations, indicate changes in the physical and chemical properties of the natural organic matter (NOM). Alteration in properties of NOM is most probably caused by increased precipitation that has changed the water pathways in the catchments and increased the leaching of organic components from the upper forest floor.