Increase In Water Transparency Research Articles

Shallow lake restoration and water quality management by the combined effects of polyaluminium chloride addition and benthivorous fish removal: a field mesocosm experiment

Polyaluminium chloride (PAC) has been used in lake restoration and water quality management as a flocculent to remove algal biomass and organic matter from the water column and increase water transparency. However, benthivorous fish may suspend the sedimented flocs and reduce the efficiency of PAC in improving water quality. Therefore, we hypothesized that PAC is more efficient in reducing algal biomass, suspended solids and total phosphorus concentrations in the water, and increasing water transparency, when benthivorous fish is removed. To test this hypothesis, we performed a field experiment combining the presence and absence of PAC (2 mg Al l−1) with the presence and absence of benthivorous fish (350 g m−2). Contrary to our hypothesis, no significant interactions were found between the effects of PAC addition and benthivorous fish removal on the measured variables. Both techniques significantly decreased chlorophyll a and phosphorus concentrations and increased water transparency, but their effects were independent of each other. The above results suggest that either of the treatments may improve water quality, but this goal would be better achieved by the combination of both techniques than by the application of one or other technique in isolation.

The effect of ice phenology exerted on submerged macrophytes through physicochemical parameters and the phytoplankton abundance

<p>The physicochemical parameters of water, the concentration of chlorophyll-<em>a</em> and the submerged aquatic vegetation (SAV) were studied to evaluate the effects of different winter seasons on the biomass of macrophytes in shallow eutrophic lakes. We hypothesised that a lack of ice cover or early ice-out can influence the physicochemical parameters of water and thus change the conditions for the development of phytoplankton and SAV. The studies were conducted in four lakes of the Western Polesie region in mid-eastern Poland after mild winters with early ice-out (MW, 2011 and 2014) and after cold winters with late ice-out (CW, 2010, 2012 and 2013). The concentrations of soluble and total nitrogen, chlorophyll-<em>a</em> and the TN:TP ratio in the lakes were considerably higher, whereas the concentration of soluble and total phosphorus and water transparency were significantly lower after the MW compared with after the CW. No differences were found in water temperature, reaction and electrolytic conductivity. Low water turbidity linked with low concentration of chlorophyll-<em>a</em> after the CW resulted in increased water transparency and the total biomass of the SAV. The negative effect of the MW on the macrophyte species was stronger on more sensitive species (<em>Myriophyllum spicatum</em>,<em> Stratiotes aloides</em>) compared with shade tolerant <em>Ceratophyllum demersum</em>. Our findings show that the ice cover phenology affected by climate warming can change the balance between phytoplankton and benthic vegetation in shallow eutrophic lakes, acting as a shift between clear and turbid water states. We speculate that various responses of macrophyte species to changes in the water quality after two winter seasons (CW and MW) could cause alterations in the vegetation biomass, particularly the expansion of shade tolerance and the decline of light-demanding species after a series of mild winters.</p>

The divergence of chlorophyll dynamics in the Naroch lakes

We present results of the analysis of long-term chlorophyll a dynamics in the Naroch lakes. It has been shown that an increase in nutrient load in the 1970s resulted in progressive eutrophication of Naroch lakes. Then, starting in the mid-1980s, the increase in water transparency and decreases in concentrations of phosphorus and nitrogen have been occurring due to the environmental improvement program. In the 1980s, the Naroch lakes experienced a strong factor as an invasion by zebra mussel (Dreissena polymorpha Pallas). Our analysis shows that responses of all three lakes to the intensive nutrient load and further decrease in the nutrient concentration as a result of the environmental protection measures have been correlated. At the same time, different degrees of the influence of the zebra mussel invasion on the lakes are shown to lead to divergence in chlorophyll dynamics. This divergence was observed as a drastic decline in correlations between variations in chlorophyll concentrations in every Naroch lakes.

What is the influence of a reduction of planktivorous and benthivorous fish on water quality in temperate eutrophic lakes? A systematic review

Abstract Background In recent decades, many attempts have been made to restore eutrophic lakes through biomanipulation. Reducing the populations of planktivorous and benthivorous fish (either directly or through stocking of piscivorous fish) may induce ecosystem changes that increase water transparency and decrease the risk of algal blooms and fish kills, at least in the short term. However, the generality of biomanipulation effects on water quality across lake types and geographical regions is not known. Therefore, we have undertaken a systematic review of such effects in eutrophic lakes in temperate regions throughout the world. Methods Searches for literature were made using online publication databases, search engines, specialist websites and bibliographies of literature reviews. Search terms were developed in English, Danish, Dutch and Swedish. Identified articles were screened for relevance using inclusion criteria set out in an a priori protocol. To reduce the risk of bias, we then critically appraised the combined evidence found on each biomanipulation. Data were extracted on outcomes such as Secchi depth and chlorophyll a concentration before, during and/or after manipulation, and on effect modifiers such as lake properties and amounts of fish removed or stocked. Results Our searches identified more than 14,500 articles. After screening for relevance, 233 of them remained. After exclusions based on critical appraisal, our evidence base included useful data on 128 biomanipulations in 123 lakes. Of these interventions, 85% had been made in Europe and 15% in North America. Meta-analysis showed that removal of planktivores and benthivores (with or without piscivore stocking) leads to increased Secchi depth and decreased chlorophyll a concentration during intervention and the first three years afterwards. Piscivore stocking alone has no significant effect. The response of chlorophyll a levels to biomanipulation is stronger in lakes where fish removal is intense, and in lakes which are small and/or have high pre-manipulation concentrations of total phosphorus. Conclusions Our review improves on previous reviews of biomanipulation in that we identified a large number of case studies from many parts of the world and used a consistent, repeatable process to screen them for relevance and susceptibility to bias. Our results indicate that removal of planktivorous and benthivorous fish is a useful means of improving water quality in eutrophic lakes. Biomanipulation tends to be particularly successful in relatively small lakes with short retention times and high phosphorus levels. More thorough fish removal increases the efficacy of biomanipulation. Nonetheless successes and failures have occurred across a wide range of conditions.

Modeling the impact of Zebra mussels (Dreissena polymorpha) on phytoplankton and nutrients in a lowland river

The Lower Havel is an eutrophicated river-lake system where the filter feeder Dreissena polymorpha (zebra mussel) are ubiquitous. Zebra mussels are known to efficiently reduce phytoplankton and increase soluble nutrients and water transparency in waterbodies but their impacts in the ecology of the Lower Havel are unknown. To address this matter, a zebra mussel submodel was integrated in the water quality model QSim to simulate its impacts. The model simulated adequately water quality trends over time and space. The simulation results show that the mussels can potentially reduce yearly Chl-a biomass by 39%, with the higher impacts taking place during summertime. Nutrient recycling by the zebra mussels is responsible for a yearly increase of 19% in ammonium and of 5% in phosphorus in the lake water.

Primary production under hypertrophic conditions and its relationship with bacterial production

In shallow hypertrophic lakes where light availability restricts the growth of macrophytes and benthic phytoplankton, pelagic phytoplankton modulates importantly ecosystem production and the energy transfer to heterotrophic bacteria. Diel and seasonal variations in primary production (PP) were studied in the hypertrophic Albufera de Valencia (Spain). Additionally, the relationship between PP and heterotrophic bacterial production (BP) was assessed. PP was extremely high, exceeding most values reported for hypertrophic lakes to date. PP displayed marked diurnal variations defined by the solar radiation curve. Likewise, PP changed importantly across seasons. Minimum PP coincided with maximum water transparency and short water residence times in winter, whereas maximum PP was observed in late spring associated with high chlorophyll a. The spring PP maximum contrasted with the summer maximum often observed in hypertrophic lakes. When compared to spring PP values, summer PP values were lower as a result of strong nitrogen limitation. In contrast to PP, BP remained fairly constant across seasons. Nonetheless, there was a joint diminution during increased water transparency followed by an increase in early spring. Phytoplankton was always the most relevant input to particulate carbon production, but the BP/PP ratio showed clear seasonal variations. The BP/PP ratio was minimum in spring, low in summer and highest in winter. The extracellular dissolved organic carbon released by phytoplankton was sufficient to meet bacterial carbon demand in all experimental dates, suggesting that allochthonous carbon sources play a minor role in sustaining BP, though they cannot be excluded. However, we hypothesize that high availability of dissolved organic carbon might explain the lack of coupling observed between BP and PP.

Invasion of an Amazonian cichlid in the Upper Paraná River: facilitation by dams and decline of a phylogenetically related species

Biological invasions and damming are currently considered the main threats to aquatic biota. This is aggravated by the facilitative effect of damming on dispersal and establishment of non-native species. In this study, the invasion process by Geophagus proximus, an Amazonian Cichlid fish, was examined in different environments of the Upper Parana River floodplain and Itaipu Reservoir. The effect of sediment retention prompted by damming (increasing water transparency) in the invasion process was investigated, in addition to the possible effects on the phylogenetically related Satanoperca pappaterra. The invasion process of G. proximus began in upstream reservoirs (source of propagules), then this species occupied the floodplain and later dispersed into the Itaipu Reservoir, being most successful (greater abundances) in environments with high water transparency (most above 200 cm). Increased abundances of the invasive species coincide with declined abundances of S. pappaterra. Diet overlap between these species was high, but apparently related to their omnivorous–detritivorous habits. Reproductive strategies were also similar. Therefore, it appears that the main factor that favored the invasive species was the increased transparency resulted from river damming, and that some interaction with S. pappaterra may be occurring.

Application of the CNOP Method in the Shallow Lake Ecosystem

It is serious on the degradation of the shallow lake ecosystem at present, while the recovery of the macrophytes vegetations and the increase in water transparency have been the main contents of the ecological restoration. Using a two-variable model, we discuss the instability and sensitivity of the ecosystem to the finite-amplitude perturbations related to the initial condition with CNOP-I method. Results show that the linearly stable clear (turbid) water states can be nonlinearly unstable with the finite-amplitude perturbations. The results also demonstrate that the facilitation interactions between the submerged macrophytes and the water transparency are the main trigger for a shift from the turbid to the clear state.

Pelagic and Benthic Nutrient Regeneration Processes in Mussel Cultures (Mytilus edulis) in a Eutrophic Coastal Area (Skive Fjord, Denmark)

Long-line mussel farming has been proposed as a mitigation tool in eutrophic coastal areas as nutrients are removed from the ecosystem upon harvest of the crops and transferred back to land. Further mussels filter the water and thereby increase water transparency and promote benthic plant growth. Intensive mussel farming may, however, negatively affect the nutrient cycling in the local environment through nutrient regeneration in the water column and through sedimentation of biodeposits resulting in organic enrichment of the underlying sediments leading to hypoxic conditions. The objective of this study was to explore the environmental interactions of a long-line mussel farm located in a eutrophic coastal area (Skive Fjord, Denmark) by studying the nutrient cycling in the water column and sediments and assessing their contribution to the nutrient dynamics and oxygen conditions in the fjord. The mussel lines contributed with nutrients, primarily ammonium, to the pool of nutrients in the water column and the contribution increased as the biomass of mussels in the farm increased. The sedimentation of biodeposits was only slightly higher at the farm (51–86 %) compared with a reference site, and the impact on the benthic environment was limited. During most of the production cycle the farm was a net sink of N due to uptake of N in the sediments, but after 1 year, the farm became a net source of N to Skive Fjord. Mussel excretion accounted for ~82 % and sediments for ~18 % of the N released from the farm. The study shows that mitigation of nutrients by long-line mussel farming will be most efficient, if mussels are harvested within the first year of the production cycle.

Diez años de monitoreo limnológico de un lago natural modificado en los trópicos: el lago Cote, Costa Rica.

It is located 650m above sea level along the boundary between the North Caribbean and Pacific slopes, near the Southern end of the volcanic Guanacaste mountain range. In the early 1980s the lake's main outlet was dammed and the outflow was diverted into Arenal Reservoir. Lake Cote was first studied in 1990-1991, and later in 2001, before it was again modified by raising its dam by one meter to use its outflow for hydroelectricity. From 2002 to 2010 it has been monitored twice a year for changes in its limnology. Here I present a summary of its basic characteristics and an analysis of their changes through time. The lake is discontinuous polymictic, and sometimes develops a thermocline at 6m depth that may last for several days as evidenced by the occasional development of an anoxic layer close to the bottom. Since its modification for hydropower production, the surface water temperature has attained higher values than before. Oxygen levels in the lake show periods of hypoxia to anoxia in the hypolimnion, that have become more frequent since modification. Despite its turbid water, the lake has low levels of nutrient concentrations and of chlorophyll a. The trend in these parameters in recent times is a reduction in chlorophyll a and an increase in water transparency, implying a reduction in primary productivity. These changes are discussed in relationship with anthropogenic factors such as the modification of the lake and its management, changes in landscape around the lake and global climate change.

The impact of a mussel farm on water transparency in the Kiel Fjord

Mussel farming is a highly discussed opportunity for inner coastal management measures to counteract the eutrophication of the Baltic Sea. There is currently a lack of detailed feasibility analyses for mussel aquaculture in German coastal waters. In 2010, a blue mussel (Mytilus edulis) farm began operating in the Kiel Fjord. In this study, we present an analysis combining measurements from this farm with a 3D-circulation and ecosystem model. We show that the mussel farm in the Kiel Fjord is incapable of producing harvests as large as farms in Swedish coastal waters. We assess and formulate the impact of the mussel farm on water transparency and calculate the attenuation coefficient and the Secchi depth from model data. Although water quality improvements are low due to the size of the farm, our results show that the area of increased water transparency is not limited to the farm area and even reaches the shoreline. We also examine the economic feasibility of the mussel farm and calculate the size of farm area, necessary to remove 10% of the riverine nutrient loads into the Kiel Fjord. We conclude that mussel farming can be a suitable supporting measure to improve water quality by removing nutrients and increasing water transparency in Kiel Fjord.

The role of charophytes in a Mediterranean pond created for restoration purposes

A small, shallow basin was created and flooded with groundwater in a Reserve Area in Albufera de València Natural Park (AVNP) under the scope of a restoration program intended to mimic typical environments such as freshwater springs, abundant in the past but currently suffering from deterioration (desiccation, pollution, etc.), with the ultimate goal of increasing local biodiversity of submerged macrophytes, particularly charophytes. In this study we have monitored, from April 2009 (a few months after its first flooding) to September 2012, the dynamics of charophyte growth and related physical, chemical and biotic variables to highlight the factors determining charophyte success. Just after flooding, five charophyte species grew spontaneously when oospores germinated in the sediments. Chara hispida populations largely dominated the community and developed dense meadows that covered virtually the entire pond floor. Charophytes exerted a negative influence on phytoplankton densities, increasing water transparency. C. hispida stands precipitated substantial CaCO3 in the form of incrustations on the plants, accompanied by coprecipitation of inorganic phosphorus, maintaining low concentrations of soluble P in the water. Reduced groundwater inflow, increased salinity, nutrient concentration, turbidity and augmented feeding pressure by waterfowl, separately or by synergistic effects, considerably reduced charophyte development during the final year of the study; however, charophytes still represent one of the most extensive and dense stands of submerged vegetation within AVNP, verifying the achievement of the goal of the restoration plan. The knowledge obtained has allowed us to recommend several measures to counteract the decrease of charophytes, which can also be applied in other regions affected by the same stressors.

Contourization and its features in technoecosystems

The phenomenon of shift in the main production-destruction processes from pelagic to bottom subsystem (contour biotopes) has different names and interpretations depending on the different "triggers" of the process. This phenomenon should be regarded as a process of contourization, which emphasizes the strengthening of the role of contour groups (benthos and periphyton). The introduction of the Zebra mussel (Dreissena polymorpha) in the cooling reservoir of Khmelnitsky nuclear power plant (NPP) (Ukraine) has led to a significant increase in water transparency and abundance of filamentous algae and other macrophytes. The increase in the abundance of contourobionts caused significant biological disturbances in the operation of equipment associated with the water intake of the NPP.

Long-term changes in the flora and vegetation of Lake Mikołajskie (Poland) as a result of its eutrophication

Changes in littoral flora as well as aquatic and swamp vegetation were analysed with increasing eutrophication of the mesotrophic Lake Mikołajskie. Over 30 years the habitat conditions of the lake deteriorated and the phy-tolittoral was reduced from a zone 6 metres wide to one of only 2 metres. In addition, the number of submerged macrophyte species decreased by 50% and the frequency of most of the remaining species declined severalfold. No new species were encountered. Species retreating from the lake littoral included all <em>Chara</em> species, <em>Potamogeton obtusifolius</em>, <em>P. natans</em> and <em>Hydrocharis morsus-ranae</em>. A significant lowering of the phytosociological diversity and species richness of aquatic and swamp communities was observed. By 1994, six of the 12 associations identified in 1964 and representing the submerged and floating-leaved vegetation (e.g. <em>Nitellopsidetum ubtusae</em>, <em>Charetum asperae</em> and <em>Potamogetonetum compressi</em>) were no longer present. In turn, 6 swamp communities from among the original 14 identified in the lake were lacking (e.g. <em>Typhetum angustifoliae</em>, <em>Sugittario-Sparganietum emersi</em> and <em>Eleocharitetum palustris</em>). At the same time, two new aquatic and swamp communities appeared (<em>Ranunculetum circinuti</em>, <em>Myriophylletum spicati</em>, <em>Caricetum acutiformis</em> and <em>Caricetum distichae</em>). In contrast there was an increase in the species richness of reedswamp communities due to an influx of marshland species. While the 1990s witnessed a distinct decrease in concentrations of nutrients in Lake Mikołajskie, the consequent increase in water transparency was not associated with an increase in the area of submerged macrophytes, or the species richness of aquatic vegetation.

Natural dimictic and polymictic lakes: similarities and differences in relationships among chlorophyll, nutrients, Secchi depth, and aquatic macrophytes

Fourteen lakes, situated in the Borecka Forest, Poland and including 8 dimictic and 6 polymictic lakes, were investigated over a period of 10 years. The water bodies were at low risk from eutrophication. A positive and statistically significant correlation between total phosphorus (TP) and total nitrogen (TN) concentrations and chlorophyll levels was reported in all of the studied lakes. The results of the study validate the hypothesis that aquatic vegetation in lakes may have a delayed response to nutrient supply because the phosphorus delivered to and present in lakes may be partially unavailable for producers. Redundancy analysis (RDA) results revealed a significant correlation between relative plant abundance and chlorophyll concentrations and a weaker relationship with the remaining lake parameters (TP, Secchi depth, TN). The positive correlation between chlorophyll and seston concentrations was significant only in dimictic lakes (r = 0.62, p = 0.001). In polymictic water bodies, chlorophyll levels decreased with Secchi depth, whereas chlorophyll concentrations in dimictic lakes varied irregularly with an increase in water transparency. The correlation between seston and Secchi depth was significant in all lakes. Seston distribution in response to a drop in water transparency did not differ significantly between the lake types. The analyzed parameters supported the identification of two groups of lakes which correspond to habitat types of the Natura 2000 network.

Responses of foraminiferal assemblages to ENSO climate patterns on bank reefs of northern Bahia, Brazil: A 17-year record

Benthic Foraminifera were assessed in Rose Bengal-stained sediment samples collected annually from 1995 to 2011 at four shallow bank reefs in Northern Bahia (Brazil). The assemblage was represented by 284 species and 88 genera, the most diverse genera being Quinqueloculina (46 spp.), Triloculina (24 spp.), Articulina (13 spp.), Textularia (11 spp.), and Elphidium (10 spp.). Significant differences in densities of live foraminifers in the sediments were observed among years, though not between reefs. Mean densities and diversities declined by ∼90% during the 1997–8 El Niño event compared with the two previous years, then rebounded during the strong La Niña years of 1999–2000, with rapid recovery of populations of small, heterotrophic foraminifers in the assemblage. After 2000, mean densities and diversities fluctuated, with lows following both the 2006–7 and 2009–10 weak El Niño events, but not so pronounced as during the 1997–8 event. Multivariate analysis clearly formed four separate groupings representing strong (hot, dry) and weak El Niño (dry) years, “normal” years, and strong La Niña (high rainfall) years. The FoRAM Index (FI), which is a single-metric index for water quality associated with reef accretion, provided additional insights into assemblage responses. The FI compares relative abundances of three functional groups of benthic foraminifers: characteristic reef-dwelling larger foraminifers that host algal endosymbionts, the ubiquitous heterotrophic smaller taxa, and specifically stress-tolerant heterotrophic taxa. The striking decline in overall densities during El Niño years likely reflects reduced food supply for the heterotrophic taxa, associated with higher temperatures and reduced runoff. Decline in the taxa that host algal symbionts is consistent with reports of extensive coral bleaching, likely related to photo-oxidative stress caused by higher temperatures and increased water transparency. The significant changes in assemblage structure and composition recorded during this 17-year study demonstrate the major influence of climatic variability associated with the El Niño/La Niña-Southern Oscillation.

Water Transparency Drives Intra-Population Divergence in Eurasian Perch (Perca fluviatilis)

Trait combinations that lead to a higher efficiency in resource utilization are important drivers of divergent natural selection and adaptive radiation. However, variation in environmental features might constrain foraging in complex ways and therefore impede the exploitation of critical resources. We tested the effect of water transparency on intra-population divergence in morphology of Eurasian perch (Perca fluviatilis) across seven lakes in central Sweden. Morphological divergence between near-shore littoral and open-water pelagic perch substantially increased with increasing water transparency. Reliance on littoral resources increased strongly with increasing water transparency in littoral populations, whereas littoral reliance was not affected by water transparency in pelagic populations. Despite the similar reliance on pelagic resources in pelagic populations along the water transparency gradient, the utilization of particular pelagic prey items differed with variation in water transparency in pelagic populations. Pelagic perch utilized cladocerans in lakes with high water transparency and copepods in lakes with low water transparency. We suggest that under impaired visual conditions low utilization of littoral resources by littoral perch and utilization of evasive copepods by pelagic perch may lead to changes in morphology. Our findings indicate that visual conditions can affect population divergence in predator populations through their effects on resource utilization.

Restoring macrophyte diversity in shallow temperate lakes: biotic versus abiotic constraints

Although many lake restoration projects have led to decreased nutrient loads and increased water transparency, the establishment or expansion of macrophytes does not immediately follow the improved abiotic conditions and it is often unclear whether vegetation with high macrophyte diversity will return. We provide an overview of the potential bottlenecks for restoration of submerged macrophyte vegetation with a high biodiversity and focus on the biotic factors, including the availability of propagules, herbivory, plant competition and the role of remnant populations. We found that the potential for restoration in many lakes is large when clear water conditions are met, even though the macrophyte community composition of the early 1900s, the start of human-induced large-scale eutrophication in Northwestern Europe, could not be restored. However, emerging charophytes and species rich vegetation are often lost due to competition with eutrophic species. Disturbances such as herbivory can limit dominance by eutrophic species and improve macrophyte diversity. We conclude that it is imperative to study the role of propagule availability more closely as well as the biotic interactions including herbivory and plant competition. After abiotic conditions are met, these will further determine macrophyte diversity and define what exactly can be restored and what not.

Influence of net-cage fish farming on zooplankton biomass in the Itá reservoir, SC, Brazil

OBJECTIVES: This study aimed to verify the influence of net-cage fish farming on zooplankton biomass in the Itá reservoir (Uruguay River, Brazil). METHODS: Samples were collected monthly from October/2009 to May/2010 at the surface and at the bottom in two sampling stations, the net-cage area and in a control area using a Van Dorn bottle and a plankton net (68 µm). RESULTS: The Cladocera and Copepoda biomass was estimated by dry weight using a micro-analytical balance, and the Rotifera biomass by Biovolume. Total zooplankton biomass varied between 6.47 and 131.56 mgDW.m-3 Calanoida copepod presented the highest value of biomass (127.56 mgDW.m-3) and rotifers, despite having an important contribution to total density, showed a maximum biomass of 2.01 mgDW.m-3. Zooplankton biomass at the net-cage area surface was higher when compared with the control area during the months of October to January. However, the zooplankton biomass was similar at the bottom of the two areas throughout the studied period. From February until May, zooplankton biomass decreased in both sampling stations, a fact probably associated with the flushing of the reservoir, followed by an increase in water transparency and a decrease in chlorophyll-a concentration in the following months (February to May). CONCLUSIONS: The influence of fish farming on zooplankton biomass was detected at the surface of the net-cage area only from October to January. From February to May this influence was not found, probably by the influence of the flushing of the reservoir.

Regime shift from phytoplankton to macrophyte dominance in a large river: Top-down versus bottom-up effects

The lower Ebro River (Catalonia, Spain) has recently undergone a regime shift from a phytoplankton-dominated to a macrophyte-dominated system. This shift is well known in shallow lakes but apparently it has never been documented in rivers. Two initial hypotheses to explain the collapse of the phytoplankton were considered: a) the diminution of nutrients (bottom-up); b) the filtering effect due to the colonization of the zebra mussel (top-down). Data on water quality, hydrology and biological communities (phytoplankton, macrophytes and zebra mussel) was obtained both from existing data sets and new surveys. Results clearly indicate that the decrease in phosphorus is the main cause of a dramatic decrease in chlorophyll and large increase in water transparency, triggering the subsequent colonization of macrophytes in the river bed. A Generalized Linear Model analysis showed that the decrease in dissolved phosphorus had a relative importance 14 times higher than the increase in zebra mussel density to explain the variation of total chlorophyll. We suggest that the described changes in the lower Ebro River can be considered a novel ecosystem shift. This shift is triggering remarkable changes in the biological communities beyond the decrease of phytoplankton and the proliferation of macrophytes, such as massive colonization of Simulidae (black fly) and other changes in the benthic invertebrate communities that are currently investigated.