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Lake Ellesmere/Te Waihora is one of New Zealand’s largest coastal, brackish water lakes. It has nationally significant wetland bird populations and is regionally important for iwi. The lake regularly experiences fluctuations in water level, resulting in a continually expanding and contracting littoral zone. This study investigated the impacts of these water level changes on the ecology of the lake. Water chemistry results collected over 12 months, confirm the lake is hypertrophic, due to high nutrient (nitrogen and phosphorus) concentrations resulting in high chlorophyll a levels and low water clarity. Water chemistry conditions were collected at five locations around the lake and showed marked spatial variation, with the eastern most end (Kaituna Lagoon) having generally the best water quality and lowest salinity (mean 4.9 ppt). Mean concentrations of total nitrogen ranged from 1.63 to 2.4 mg/L, chlorophyll a from 50 to 148 ug/L and total suspended solids from 151 – 248 mg/L. Seasonally, highest nutrient concentrations (mean, total nitrogen = 2.625 mg/L, dissolved reactive phosphorus = 0.059 mg/L and total phosphorus = 0.365 mg/L) occurred in late summer months (February – March), slightly decreasing but remaining high throughout winter. The benthic invertebrate community was surprisingly diverse, Crustacea (Paracorophium excavatum), Oligochaeta, Mollusca (Potamopyrgus antipodarum) and Chironomidae (Chironomus zealandicus) were dominant community members in the littoral zone, although 24 other taxa were collected. At high water levels, taxonomic richness increased in the eulittoral zone, while decreasing in the mid-littoral and lower littoral zones. In contrast, density decreased with higher water level in the eulittoral and mid-littoral zones, while increasing in the lower littoral zone. Benthic invertebrate communities appeared to be adapted to periods of intermittent dewatering, and even sustained dewatering under cooler temperatures. Despite the relatively high diversity of benthic invertebrates, invertebrate predators are generally absent from the lake. My results suggest multiple factors and interactions from predation pressure, salinity and lack of macrophytes are likely responsible for the absence of predatory invertebrates such as damselfly (Xanthocnemis zealandica) and dragonfly (Procordulia grayi) larvae. The lack of significant relationships between water quality variables and water level, and the positive relationship between chlorophyll a and salinity, suggests that current lake opening events do not have a positive effective on either water quality or phytoplankton biomass in Lake Ellesmere/Te Waihora. However, the current lake opening regime seems to be favourable to benthic invertebrate survival in the littoral zone, as the lake is predominantly open over winter when temperatures are lower, reducing the risk of desiccation. Anthropogenic activities which modify hydrodynamic and water quality conditions can potentially have a large negative impact on the structure and diversity of the littoral invertebrate community as well as flow on effects through the lake food web. Based on results from this study, I suggest a minimum lake level at Taumutu of 0.6 m during the months from November – April in order to protect benthic invertebrate communities in the eulittoral zone from extensive loss of habitat, extreme temperature and reduced risk of desiccation. Having a minimum set at ~0.6 m would provide sufficient littoral zone habitat for the lakes extensive bird life and fish populations. In addition, immediate efforts are needed into reducing nutrient loads into the lake, through improved farm management (nutrient and stocking budgets) and riparian fencing. Furthermore, physical and chemical water quality properties would benefit from an increased water level over summer months, by reducing water temperatures, diluting readily available nutrient concentrations and potentially reducing phytoplankton (and potentially toxic cyanobacterial) blooms.

Este estudo foi realizado com base em coletas sazonais no período de um ano (2010-2011), em três pontos na Lagoa do Peixe e um ponto na Lagoa do Ruivo, lagoa à montante, com objetivo de avaliar a existência de padrões espaciais e/ou sazonais na estrutura fitoplanctônica. Este ambiente lagunar subtropical está incluso no Parque Nacional da Lagoa do Peixe (sul do Brasil) e é conectado ao Oceano Atlântico por uma barra de areia localizada na porção central da laguna. A salinidade variou amplamente de condições limnéticas à euhalinas, sendo observada em média, salinidade mais baixa no inverno, e mais elevada no verão, exceto na Lagoa do Ruivo no verão, que mostrou tendência oposta. Em relação à espacialidade, a salinidade apresentou tendência à um gradiente crescente dos pontos extremos da laguna em direção a barra, apresentando menor variação nesta (mesohalino à euhalino). A comunidade fitoplanctônica esteve formada por sete classes com 136 táxons genéricos à infra-específicos. A densidade variou de 653 a 114.829 ind.mL-1, sendo os menores valores registrados próximos a barra. Os grupos abundantes em relação a densidade foram as cianobactérias e diatomáceas. A biomassa variou de 0,3 a 24,1 mg.L-1, sendo o menor valor registrado no inverno e o maior no outono, ambos próximo a barra. A elevada biomassa no outono ocorreu devido o predomínio de euglenofíceas. Espacialmente, a Lagoa do Ruivo (menor salinidade) apresentou maior riqueza. O grupo das diatomáceas apresentou a maior riqueza total. Análises de ordenação (ACP, RDA e ACC) para verificação de tendências sazonais e/ou espaciais foram realizadas, sugerindo existência de tendências a padrões, tanto sazonais, quando espaciais na estrutura e distribuição fitoplanctônica do sistema lagunar da Lagoa do Peixe, onde a salinidade foi a variável que contribui para estes gradientes. / This study was based on seasonal sampling during one year (2010-2011) at three points in Peixe Lagoon and one point in Ruivo Lagoon, located upstream, to evaluate the spatial and seasonal patterns of phytoplankton communities. These subtropical lagoon environments are included in the National Park of Peixe Lagoon (southern Brazil) and are connected to the Atlantic Ocean by a sand bar located at the central portion of the lagoon. Salinity ranged widely from limnetic to euhaline conditions, on average from lower salinity in winter to higher in summer being observed, except at Ruivo Lagoon in summer, which showed an opposite trend. Regarding spatiality, salinity tended to an increasing gradient from extreme points of the lagoon toward the bar, with less variation at this points (mesohaline to euhaline). The phytoplankton taxonomic community was composed of seven classes with 136 generic to infraspecific taxa. Density ranged from 653 to 114,829 ind.mL-1, with the lowest values recorded near the bar. The most abundant groups in density were cyanobacteria and diatoms. Biomass ranged from 0.3 to 24.1 mg.L-1, with the lowest value recorded in winter and higher, in the fall, both near the bar. The high biomass in fall was due to the predominance of euglenoids. Spatially, the Ruivo Lagoon (lower salinity) showed greater richness. Diatoms groups showed the highest total richness. Ordination analysis (PCA, RDA and CCA) were performed, suggesting the existence seasonal and spatial patterns in relation to the structure and distribution in phytoplankton of this lagoon system, where salinity was the variable that most contributed to these gradients.

Este estudo foi realizado com base em coletas sazonais no período de um ano (2010-2011), em três pontos na Lagoa do Peixe e um ponto na Lagoa do Ruivo, lagoa à montante, com objetivo de avaliar a existência de padrões espaciais e/ou sazonais na estrutura fitoplanctônica. Este ambiente lagunar subtropical está incluso no Parque Nacional da Lagoa do Peixe (sul do Brasil) e é conectado ao Oceano Atlântico por uma barra de areia localizada na porção central da laguna. A salinidade variou amplamente de condições limnéticas à euhalinas, sendo observada em média, salinidade mais baixa no inverno, e mais elevada no verão, exceto na Lagoa do Ruivo no verão, que mostrou tendência oposta. Em relação à espacialidade, a salinidade apresentou tendência à um gradiente crescente dos pontos extremos da laguna em direção a barra, apresentando menor variação nesta (mesohalino à euhalino). A comunidade fitoplanctônica esteve formada por sete classes com 136 táxons genéricos à infra-específicos. A densidade variou de 653 a 114.829 ind.mL-1, sendo os menores valores registrados próximos a barra. Os grupos abundantes em relação a densidade foram as cianobactérias e diatomáceas. A biomassa variou de 0,3 a 24,1 mg.L-1, sendo o menor valor registrado no inverno e o maior no outono, ambos próximo a barra. A elevada biomassa no outono ocorreu devido o predomínio de euglenofíceas. Espacialmente, a Lagoa do Ruivo (menor salinidade) apresentou maior riqueza. O grupo das diatomáceas apresentou a maior riqueza total. Análises de ordenação (ACP, RDA e ACC) para verificação de tendências sazonais e/ou espaciais foram realizadas, sugerindo existência de tendências a padrões, tanto sazonais, quando espaciais na estrutura e distribuição fitoplanctônica do sistema lagunar da Lagoa do Peixe, onde a salinidade foi a variável que contribui para estes gradientes. / This study was based on seasonal sampling during one year (2010-2011) at three points in Peixe Lagoon and one point in Ruivo Lagoon, located upstream, to evaluate the spatial and seasonal patterns of phytoplankton communities. These subtropical lagoon environments are included in the National Park of Peixe Lagoon (southern Brazil) and are connected to the Atlantic Ocean by a sand bar located at the central portion of the lagoon. Salinity ranged widely from limnetic to euhaline conditions, on average from lower salinity in winter to higher in summer being observed, except at Ruivo Lagoon in summer, which showed an opposite trend. Regarding spatiality, salinity tended to an increasing gradient from extreme points of the lagoon toward the bar, with less variation at this points (mesohaline to euhaline). The phytoplankton taxonomic community was composed of seven classes with 136 generic to infraspecific taxa. Density ranged from 653 to 114,829 ind.mL-1, with the lowest values recorded near the bar. The most abundant groups in density were cyanobacteria and diatoms. Biomass ranged from 0.3 to 24.1 mg.L-1, with the lowest value recorded in winter and higher, in the fall, both near the bar. The high biomass in fall was due to the predominance of euglenoids. Spatially, the Ruivo Lagoon (lower salinity) showed greater richness. Diatoms groups showed the highest total richness. Ordination analysis (PCA, RDA and CCA) were performed, suggesting the existence seasonal and spatial patterns in relation to the structure and distribution in phytoplankton of this lagoon system, where salinity was the variable that most contributed to these gradients.

Este estudo foi realizado com base em coletas sazonais no período de um ano (2010-2011), em três pontos na Lagoa do Peixe e um ponto na Lagoa do Ruivo, lagoa à montante, com objetivo de avaliar a existência de padrões espaciais e/ou sazonais na estrutura fitoplanctônica. Este ambiente lagunar subtropical está incluso no Parque Nacional da Lagoa do Peixe (sul do Brasil) e é conectado ao Oceano Atlântico por uma barra de areia localizada na porção central da laguna. A salinidade variou amplamente de condições limnéticas à euhalinas, sendo observada em média, salinidade mais baixa no inverno, e mais elevada no verão, exceto na Lagoa do Ruivo no verão, que mostrou tendência oposta. Em relação à espacialidade, a salinidade apresentou tendência à um gradiente crescente dos pontos extremos da laguna em direção a barra, apresentando menor variação nesta (mesohalino à euhalino). A comunidade fitoplanctônica esteve formada por sete classes com 136 táxons genéricos à infra-específicos. A densidade variou de 653 a 114.829 ind.mL-1, sendo os menores valores registrados próximos a barra. Os grupos abundantes em relação a densidade foram as cianobactérias e diatomáceas. A biomassa variou de 0,3 a 24,1 mg.L-1, sendo o menor valor registrado no inverno e o maior no outono, ambos próximo a barra. A elevada biomassa no outono ocorreu devido o predomínio de euglenofíceas. Espacialmente, a Lagoa do Ruivo (menor salinidade) apresentou maior riqueza. O grupo das diatomáceas apresentou a maior riqueza total. Análises de ordenação (ACP, RDA e ACC) para verificação de tendências sazonais e/ou espaciais foram realizadas, sugerindo existência de tendências a padrões, tanto sazonais, quando espaciais na estrutura e distribuição fitoplanctônica do sistema lagunar da Lagoa do Peixe, onde a salinidade foi a variável que contribui para estes gradientes. / This study was based on seasonal sampling during one year (2010-2011) at three points in Peixe Lagoon and one point in Ruivo Lagoon, located upstream, to evaluate the spatial and seasonal patterns of phytoplankton communities. These subtropical lagoon environments are included in the National Park of Peixe Lagoon (southern Brazil) and are connected to the Atlantic Ocean by a sand bar located at the central portion of the lagoon. Salinity ranged widely from limnetic to euhaline conditions, on average from lower salinity in winter to higher in summer being observed, except at Ruivo Lagoon in summer, which showed an opposite trend. Regarding spatiality, salinity tended to an increasing gradient from extreme points of the lagoon toward the bar, with less variation at this points (mesohaline to euhaline). The phytoplankton taxonomic community was composed of seven classes with 136 generic to infraspecific taxa. Density ranged from 653 to 114,829 ind.mL-1, with the lowest values recorded near the bar. The most abundant groups in density were cyanobacteria and diatoms. Biomass ranged from 0.3 to 24.1 mg.L-1, with the lowest value recorded in winter and higher, in the fall, both near the bar. The high biomass in fall was due to the predominance of euglenoids. Spatially, the Ruivo Lagoon (lower salinity) showed greater richness. Diatoms groups showed the highest total richness. Ordination analysis (PCA, RDA and CCA) were performed, suggesting the existence seasonal and spatial patterns in relation to the structure and distribution in phytoplankton of this lagoon system, where salinity was the variable that most contributed to these gradients.

Improved knowledge of sediment dynamics within a lake system is important for understanding lake water quality. This research was focused on an assessment of the vertical sediment flux in Lake Jesup, a shallow (1.3 m average depth) hypereutrophic lake of central Florida. Sediment dynamics were assessed at varying time scales (daily to weekly) to understand the transport of sediments from external forces; wind, waves, precipitation and/or runoff. Four stations were selected within the lake on the basis of water depth and the thicknesses of unconsolidated (floc) and consolidated sediments. At each of these stations, a 10:1 (length to diameter) high aspect ratio trap (STHA) was deployed to collect particulate matter for a one to two week period. The water and sediment samples were collected and analyzed for total carbon (TC), total phosphorus (TP) and total nitrogen (TN). Mass accumulation rates (MAR) collected by the traps varied from 77 to 418 g m-2 d-1 over seven deployments. TN, TP and TC sediment concentrations collected by the traps were consistently higher than the sediments collected by coring the lake bottom and is most likely associated with water column biomass. A yearly nutrient budget was determined from August 2009 to August 2010 with flux calculated as 2,033,882 mt yr-1.

Alguns estudos mostraram que heterópteros aquáticos podem influenciar a estrutura de comunidades zooplanctônicas. No entanto, parte destes estudos foram realizados em experimentos de laboratório que não são capazes de simular totalmente a estrutura do ecossistema. Para confrontar este problema, técnicas moleculares juntamente com experimentos in situ podem ser adotados. A técnica molecular baseia-se na detecção de DNA das presas (biomarcadores) no tubo digestório dos predadores. O objetivo deste trabalho foi analisar o conteúdo estomacal dos heterópteros Martarega uruguayensis e Rheumatobates crassifemur visando avaliar a hipótese da presença de presas zooplanctônicas por meio de vestígios de DNA , bem como avaliar a existência do efeito da predação dos notonectídeos sobre a densidade populacional das presas no ambiente. Para atender aos objetivos propostos, o trabalho foi dividido em 3 capítulos: O capítulo I descreve como foram escolhidos os biomarcadores moleculares das presas e o desenvolvimento dos primers necessários para conduzir as análises. Os primers específicos são de regiões internas do gene COI das presas zooplanctônicas. Foram testadas suas especificidades e sensibilidade por meio de reações de PCR. Em testes de especificidade, todos os primers amplificaram com êxito o biomarcador das presas-alvo, sendo incapazes de amplificar o biomarcador de qualquer outra espécie testada. Em testes de sensibilidade, os primers amplificaram com sucesso os biomarcadores das presas zooplanctônicas mesmo em baixas concentrações de DNA, assim como diretamente do trato digestório dos predadores; O capítulo II aborda aspectos da dieta dos predadores a partir da frequência de biomarcadores das presas encontrados nos tubos digestório dos insetos coletados no lago. Por meio de 48 reações de PCR com os primers específicos das presas-alvo foram analisados 240 tubos digestórios dos predadores. As presas com maior eletividade foram S. serrulatus e D. gessneri, e a menor foi D. cf. brevireme, apesar da alta abundância no ambiente. Tanto para gerrídeos quanto para notonectídeos há uma seletividade acentuada por espécies de presas de maior tamanho, mesmo que em menor frequência relativa no ambiente quando comparadas a outras espécies. Acredita-se que a preferência por presas maiores esteja relacionada à maior facilidade para detecção e manipulação do predador. A frequências de biomarcadores nos tubos digestórios de M. uruguayensis foi maior no período com maior disponibilidade de presas; O capítulo III avaliou, o efeito do predador M. uruguayensis (Notonectidae) sobre as densidades das populações de presas zooplanctônicas a partir de experimento em mesocosmo. No geral, não houve influência significativa dos predadores sobre nenhuma espécie nos dois primeiros dias. O efeito da predação sobre copepoditos e náuplios foi mais acentuados entre os dias 3 e 4, enquanto que para copépodos adultos foi nos dias 2 e 3. Já para os cladóceros o efeito foi mais acentuado nos dias 4 a 6, exceto para D. cf. brevireme que não teve efeito da predação em nenhum dia. Aspectos relacionados ao tamanho corporal, densidade populacional das presas, capacidade de evasão e diminuição da sobreposição entre predador e presa são fatores fundamentas no padrão de seletividade e da preferência alimentar de notonectídeos. / A few studies have shown that aquatic heteroptera can influence the structure of zooplanktonic communities. However, some of these studies have been conducted in laboratory experiments that are not able to fully simulate the structure of the ecosystem. To confront this problem, a molecular approach along with in situ experiment can be adopted. Molecular approach is based on the detection of prey DNA (biomarkers) in the digestive tract of predators. The objective of this work was to analyze the gut contents of the heteropterans Martarega uruguayensis and Rheumatobates crassifemur to test the hypothesis that will be found traces of zooplankton prey DNA, as well as the effect of the notonectid predation on population density of prey in the environment. To meet the proposed objectives, the work was divided in 3 chapters: Chapter I describes how the molecular biomarkers of prey were chosen and the development of the primers needed to conduct the analyses. The specific primers are from internal regions of the COI gene of zooplanktonic prey. Their specificities and sensibility were tested by means of PCR reactions. In specificity tests, all primers successfully amplified the target prey biomarker and were unable to amplify biomarker of any other species tested. In sensitivity tests, the primers successfully amplified the biomarkers of zooplankton prey even at low DNA concentrations, as well as directly from the digestive tract of predators; Chapter II addresses aspects of the predators diet using the frequency of biomarkers of prey found in the digestive tubes of the insects. By means of 48 PCR reactions, with the specific primers from target prey, were analyzed 240 digestive tracts of predators. The prey with greater electivity were S. serrulatus and D. gessneri, and the smaller one was D. cf. brevireme, despite the high abundance in the environment. For both gerrids and notonectids, there was a marked selectivity for larger size prey, even though at a lower relative frequency in the environment when compared to other species. This suggests that the preference for larger prey is related to the greater facility for detection and manipulation by the predator. The frequencies of biomarkers in the digestive tracts of M. uruguayensis were higher in the period with higher prey availability; Chapter III evaluated the effect of the predator M. uruguayensis on the densities of zooplankton prey populations from experiment in mesocosm. In general, there was no significant influence of predators on any species in the first two days. The effect of predation on copepodites and nauplii were more pronounced between days 3 and 4, whereas for adult copepods on days 2 and 3. The effect on cladocerans was more pronounced on days 4 to 6, except for D. cf. brevireme that was not preyed on. Aspects related to body size, population density of the prey, evasion capacity and decrease overlap between predator and prey are fundamental in the pattern of selectivity and feeding preference of notonectids.

In a changing climate, it is increasingly important to be able to model environmental effects on food webs, and to do that, one must have appropriate dynamic models. I present a shallow lake ecosystem model where producers, grazers, carnivores, piscivores, and detritivores are coupled through resource (light, nutrients and detritus) fluxes between the benthic and pelagic habitats and through carnivore life history events (ontogenetic habitat and diet shifts). The two habitats each contain primary producers, grazers, carnivores and detritivores. Within the habitats, there is strong top-down regulation, but across habitat boundaries, bottom-up interactions drive production. In the absence of piscivores, stage-structured carnivores cause intriguing patters of alternative stable states. Notably, the model predicts a lesser dependence on benthic production with detritus presence. Model predictions are largely in agreement with empirical studies. The results have implications for management of freshwater, and for the interpretation of previous models.

Ecossistemas aquáticos flutuam em torno de tendências, podendo ocorrer transições súbitas de um regime persistente para outro, alterando a viabilidade dos recursos ou dos parâmetros físico-químicos. Seguindo essa tendência, comunidades variam no tempo e no espaço como resultado de suas interações com o ambiente e com os outros organismos. Comunidades microbianas aquáticas são importantes componentes do metabolismo aquático, atuando na reciclagem de nutrientes pela remineralização e na transferência de biomassa pela alça microbiana. A compreensão da dinâmica funcional microbiana em lagos é uma importante ferramenta para o entendimento desses sistemas, uma vez que a funcionalidade e a composição microbiana podem refletir as condições gerais da lagoa em questão. Desse modo, no presente trabalho, foi utilizada a abordagem de impressões metabólicas da comunidade microbiana na Lagoa Mangueira, uma grande lagoa costeira, rasa e subtropical localizada no extremo sul do Brasil. Teve como objetivo avaliar, pioneiramente para essa região, a diversidade metabólica microbiana aquática através de padrões de consumo de fontes de carbono disponíveis, utilizando Biolog EcoplatesTM e verificar a existência de dinâmicas temporais e espaciais na preferência de consumo desses substratos. Foi observada heterogeneidade temporal e espacial na preferência de consumo de substratos ao longo da Lagoa. Tais preferências puderam ser representadas por diferentes substratos indicadores, associados às estações e aos locais da Lagoa. O consumo das fontes de carbono esteve relacionado com a variabilidade ambiental de fatores como turbidez, transparência da água, nutrientes, clorofila a, carbono orgânico temperatura. Isso evidencia que a dinâmica funcional foi influenciada pela dinâmica de nutrientes, pelos componentes de produtividade, pela sazonalidade e pela compartimentação da Lagoa. Nesse sentido, a investigação do consumo de fontes de carbono, no presente estudo, se mostrou um bom indicador da dinâmica funcional microbiana para ecossistemas aquáticos. / Aquatic ecosystems float around trends in which abrupt transitions can occur between persistents regimes, alterning the viability of the resources or the physical and chemical parameters. Following this trend, communities vary in time and space as a result of their interactions with the environment and other organisms. Microbial communities are important components in the aquatic metabolism, responsible for recycling of nutrients by remineralization, and transfering of biomass through the microbial food web. Understanding the functional microbial dynamics in lakes is an important tool to understand these systems, since the microbial composition and function may reflect the overall condition of the lake. The approach of metabolic fingerprint of microbial communities in shallow lakes was applied in the current study in Lake Mangueira, a costal and large subtropical shallow lake located in southern Brazil. The main goal was to evaluate, pioneered for this region, the heterotrophic microbial metabolic diversity through consumption patterns of available carbon sources using Biolog EcoplatesTM and verify the existence of temporal and spatial dynamics of consumption preference in these substrates. As a result, was observed temporal and spatial heterogeneity of substrate consumption preference among the Lake. Such preferences were represented by different substrate indicators, associated with seasons and sites within the Lake. The substrate utilization was related to environmental variability of factors as turbidity, water transparence, nutrients, chlorophyll a, organic carbon, water temperature. This is evidence that the functional dynamic was influenced by nutrients dynamic, production component, seasonality and compartimentation. In this way, carbon source utilization approach was a good indicator of functional dynamics in the present study to aquatic ecosystems.

Future climate in temperate regions is projected to get warmer and in many cases wetter. This poses questions about how phytoplankton in our lakes will respond. A dynamic modeling approach based on an allometric description of phytoplankton characteristics was used to investigate how the biomass of different functional groups of phytoplankton will respond to a changed future climate. Simulations based on a warmer future climate scenario suggest that we will experience an increase in phytoplankton biomass in northern temperate lakes. Moreover, phytoplankton groups are projected to shift towards a dominance of cyanobacteria at the expense of diatoms. Climate may affect phytoplankton, either via in-lake changes in temperature and stratification, or due to altered processes at the watershed level, which influence rates of nutrient export and water discharge. This study found that changes in lake temperature and stratification are the major causes of the projected increase in phytoplankton biomass, but that changes in the timing of nutrient export did influence the succession of diatoms. Variation in SPIM (suspended particulate inorganic matter) can have an important role in influencing the depth of the euphotic zone in a turbid lake, and hence the light climate experienced by phytoplankton. Wind and river discharge were found to regulate SPIM in this study, not only wind as in many other studies. Variations in SPIM could be adequately described by a few governing equations. This thesis suggests that, as a result of climate change, lakes close to the limit of becoming eutrophied may be pushed past a threshold beyond which water quality problems will become more prevalent. Finally it is important to bear in mind that all models are simplifications of the reality as we understand it. Still, the use of models can often give a good indication as to what might be expected in the future.