Making waves: The sensitivity of lakes to brownification and issues of concern in ecological status assessment

Brownification or increasing water colour is a common problem in aquatic ecosystems. It affects both physico-chemical properties and biotic communities of the impacted waters. A common view is that lakes having low background water colour are most sensitive to brownification. In this article, we show that although low-colour and high-colour lakes respond differently to brownification, the effects on biotic communities can be strong irrespective of water colour. For phytoplankton production, the effect of brownification can be positive at low colour and negative at high colour, the relative effect being strongest at high colour. For fish foraging, the disturbance per increasing unit of colour may also be highest at high-colour conditions. Additionally, the presently used classification systems mostly describe the effects of eutrophication and do not account for the effects of brownification. Studies on the whole colour range of lakes are needed and indicators used in the ecological status assessment of lakes must be developed to reveal the effects of brownification. Indicators distinguishing the effects of brownification from those of eutrophication are especially needed.

Assessment of benthic invertebrate diversity and river ecological status along an urbanized gradient using environmental DNA metabarcoding and a traditional survey method

Benthic invertebrate diversity is one of the most commonly used bioindicators for assessing aquatic ecosystem health in river systems. Although an increasing number of studies have focused on assessing benthic invertebrate diversity using environmental DNA metabarcoding and traditional survey methods, benthic invertebrate diversity and ecological status assessments performed across different landscapes within river systems have not been well documented. Here, the diversity and ecological status of benthic invertebrates and the influence of water quality on the invertebrate assemblage distribution along an urbanization gradient in rivers from the Jingjinji (JJJ) region, China, were investigated using eDNA metabarcoding and the traditional method. With the combination of the two methods, 395 benthic invertebrates from 6 phyla, 27 orders, 94 families, and 222 genera were identified. The species richness of the benthic invertebrate community in the mountain area was significantly higher than that in the urban and agricultural areas. Compared to the traditional results, eDNA metabarcoding obtained a significantly greater number of species from every sampling site (P = 0.000) and detected a notably higher abundance in Annelida (P = 0.000). Furthermore, the nonmetric multidimensional scaling (NMDS) and permutational multivariate analysis of variance (PERMANOVA) based on the Bray-Curtis dissimilarity index indicated that the benthic invertebrate communities from the different habitats were discriminated more accurately and easily using eDNA metabarcoding (P = 0.038) than with the traditional method (P = 0.829). Additionally, the assemblages identified by eDNA metabarcoding were more closely linked to water quality and could be realistically used to assess the ecological status of rivers. Our findings highlight that eDNA metabarcoding could represent a rapid and reliable method for estimating benthic invertebrate diversity and ecological status in river systems.

ZIPLAS: Zooplankton Index for Polish Lakes' Assessment: a new method to assess the ecological status of stratified lakes

Zooplankton is widely recognized as a key component of pelagic ecosystems and forms the basis for major trophic webs. Although zooplankton has often been used as an indicator of trophic state, it has not been included as an obligatory element of the water assessment systems compliant with the Water Framework Directive. This article introduces the Zooplankton Index for Polish Lakes' Assessment (ZIPLA_S) as a new method to assess the ecological status of stratified lakes based on the zooplankton community. The ZIPLA_S evaluates three aspects of zooplankton communities, namely, taxonomic composition and abundance, diversity of the zooplankton community, and stressor-sensitive species, which are combined into a multimetric index. Following are the metrics used to compose multimetric ZIPLA_S: percentage share of the Rotifer species indicative of high trophy in the indicative group's number (IHTROT; %), ratio of Calanoida to Cyclopoida individual numbers (CA/CY), percentage of tecta form in the population of Keratella cochlearis (TECTA; %), Margalef's index (d), and zooplankton abundance (NZOL; ind./L). ZIPLA_S responds clearly to eutrophication indicators-the strongest with Secchi disc visibility (Spearman's rank correlation R = 0.86) and slightly weaker with the expressed by total phosphorus (R = -0.74), total nitrogen (R = 0.68) and the catchment pressure expressed by the nutrient loads generated by different types of land use (R = -0.58).

Benthic diatom community dynamics in Mediterranean intermittent streams: Effects of water availability and their potential as indicators of dry-phase ecological status

The study of intermittent rivers is a critical and timely issue due to their worldwide increase, triggered by several causes including climate change. The need to understand the response of intermittent river biota to water intermittency led us to conduct this study using benthic diatoms collected in southern Portugal. Benthic diatoms were explored in terms of assemblages, diversity indices, the Specific Pollution Sensitivity (SPI) Index, functional metrics (i.e. ecological guilds and life-forms) and conservation status. We verified that changes in water physico-chemical characteristics were highly controlled by flow intermittency, which in turn is directly linked to meteorological variables (air temperature and precipitation). Changes in diatom assemblages reflect the aquatic regime of sites, changes in aquatic states through time and mesohabitats (dry biofilm, samples collected in pools or under flowing conditions). Species richness, on the other hand, did not reflect these differences, whilst Shannon diversity and Pielou's Evenness indices only reflected mesohabitat differences. The SPI distinguished sampling periods, and mesohabitats. The relative abundance of ecological guilds changed with aquatic states, with the low-profile guild dominating in eurheic and arheic conditions (except during Summer), being replaced by motile taxa in summer arheic conditions, reflecting increases in nutrient and siltation. The hypothesis that benthic diatom assemblages in dry biofilm can be used as an indicator of ecological status during the dry-phase was validated, since no differences between the Ecological Quality Ratio determined in dry biofilm collected in Summer 2017 and the previous Spring 2017 in flowing water. A method is proposed for diatom sampling in dry biofilm, contributing to an integrated ecological status evaluation, which considers the dry-phase and enhances the reach of biomonitoring programs.

Limited effects of pesticides on stream macroinvertebrates, biofilm nematodes, and algae in intensive agricultural landscapes in Sweden

Pesticides are frequently detected in surface waters, sometimes at levels exceeding ecotoxicological guidelines. We screened for almost 100 pesticides in 32 streams from intense agricultural areas in Southern Sweden, in concert with water chemistry parameters. In addition, we investigated the communities of benthic macroinvertebrates, biofilm nematodes and algae and calculated multiple bioassessment metrics. The number of pesticides found in each stream ranged between 2 and 52, but the sum of Toxic Units (ΣTU) for the mixtures was generally low, and exceeded the European Uniform Principles only in a single sample for algae and in 2% of the samples for Daphnia. Only nematode communities were significantly correlated with the ΣTU, potentially due to their higher pesticide exposure in biofilms. Diatom metrics showed that most streams were impacted by eutrophication and macroinvertebrate metrics showed good status in most streams, whereas the SPEAR_pesticides (SPEcies At Risk) index, specifically designed to indicate pesticide effects, showed that about half of the samples were at risk. Interestingly, SPEAR_pesticides was not correlated to ΣTU_Daphnia, and this discrepancy suggests that redefining the boundaries for quality classes might be necessary for this index. Moreover, SPEAR_pesticides was positively correlated with the commonly used macroinvertebrate index ASPT, although disparate results were found for several streams. We argue that this questions the scaling of both metrics and the specificity of their responses. We discuss that the overall good/moderate status of the streams, despite the intense agriculture in the catchments, can be due to the fact that i) a sampling strategy with repeated grab samples did not capture peak pesticide concentrations, thus underestimating acute exposure, ii) pesticide run-off indeed was low, due to measures such as buffer strips, and iii) the nutrient-rich conditions and high sediment loads counteracted pesticide toxicity. We conclude that agricultural land use was the overriding stressor in the investigated streams, including strong effects of nutrients, less apparent effects of pesticides and likely impact of hydromorphological alterations (not specifically addressed in this study).

Sediment nutrients, ecological status and restoration of lakes

Phosphorus (P) is the main nutrient that causes eutrophication in fresh waters. The majority of P in lake ecosystems is usually stored in the bottom sediment, hence P cycling from the sediment into the water column can significantly and negatively impact water quality. However, sediment nutrients are not taken into account, for instance, in the ecological status assessment determined by the European Water Framework Directive. This encourages lake managers to improve the water quality at the expense of the sediment; for example, chemical inactivation of P has been applied to the sediment in numerous lakes for rapid water quality improvement. While this may generate immediate results, inactivation of sediment P may in fact delay the long-term recovery of lake ecosystems and inhibit the re-use of nutrients. In some specific cases, these rapid restoration efforts that compromise sediment quality are justified. Nevertheless, we should aim for a general strategy that can promote permanent recovery of lake ecosystems - including their sediments. The support for such restoration activities may be difficult to find, since the tangible outcome is realized only after long periods of time.

Probability of misclassifying biological elements in surface waters

Measurement uncertainties are inherent to assessment of biological indices of water bodies. The effect of these uncertainties on the probability of misclassification of ecological status is the subject of this paper. Four Monte-Carlo (M-C) models were applied to simulate the occurrence of random errors in the measurements of metrics corresponding to four biological elements of surface waters: macrophytes, phytoplankton, phytobenthos, and benthic macroinvertebrates. Long series of error-prone measurement values of these metrics, generated by M-C models, were used to identify cases in which values of any of the four biological indices lay outside of the "true" water body class, i.e., outside the class assigned from the actual physical measurements. Fraction of such cases in the M-C generated series was used to estimate the probability of misclassification. The method is particularly useful for estimating the probability of misclassification of the ecological status of surface water bodies in the case of short sequences of measurements of biological indices. The results of the Monte-Carlo simulations show a relatively high sensitivity of this probability to measurement errors of the river macrophyte index (MIR) and high robustness to measurement errors of the benthic macroinvertebrate index (MMI). The proposed method of using Monte-Carlo models to estimate the probability of misclassification has significant potential for assessing the uncertainty of water body status reported to the EC by the EU member countries according to WFD. The method can be readily applied also in risk assessment of water management decisions before adopting the status dependent corrective actions.

Ecological quality status of the Adriatic coastal waters evaluated by the organotin pollution biomonitoring

The aim of this study was to evaluate the post-legislation change in tributyltin (TBT) pollution at Croatian Adriatic coast. Gastropod Hexaplex trunculus and sediments were collected, nearly 10years after TBT based antifouling paints were banned, at 12 locations along the coast where a previous study was conducted in 2005. The study showed a decline of TBT levels over the investigated period, although all gastropods populations were highly affected by imposex meaning that prohibition did not result in the recovery of populations. The further aim was to propose the Ecological Quality Ratio (EQR) boundaries for potential use of H. trunculus as a principal bioindicator in the assessment of the ecological status of the Mediterranean regarding TBT pollution, under the Water Framework Directive (WFD). According to the proposed EQR classes, the WFD target for achieving the Good ecological status of the marine environment by 2015 was not reached.