Microbial - Planktonic foodweb dynamics of a eutrophic Area of Concern: Hamilton Harbour

<p>Hamilton Harbour, located on the western end of Lake Ontario, has a long history of cultural eutrophication as well as industrial contamination. We explored the structure and function of the microbial – planktonic foodweb during the growing seasons (May–October) of 2004 and 2006 in order to consider the flow of autochthonous production from lower to higher trophic levels. Our analyses included microscope based assessments of bacteria, heterotrophic nanoflagellates, ciliates, phytoplankton and zooplankton as well as radioisotope based measurements of primary productivity and bacterial growth. While routine measures of total phosphorus (avg: 25–33 µg l⁻¹) and chlorophyll <i>a</i> (avg: 12–15 µg l⁻¹) were indicative of eutrophy, mean phytoplankton biomass in 2004 (2.0 g m⁻³) and 2006 (2.2 g m⁻³) suggested mesotrophic conditions. However, the appearance of algal blooms in the summer of 2006 was an obvious indicator of cultural eutrophication. With respect to the microbial – planktonic foodweb, the organic carbon pool increased from a mean of 757.5 mg C m⁻³ in 2004 to 1160.3 mg C m⁻³ in 2006 and this increase was almost evenly split between autotrophs (198.7 mg C m⁻³) and heterotrophs (204.1 mg C m⁻³). The increased autotrophic carbon is readily attributable to the observed algal blooms driven by warmer temperatures and higher concentrations of soluble reactive phosphorus. However, the increase in heterotrophic carbon, primarily heterotrophic nanoflagellates, was apparent from the earliest observations in 2006 and remained consistently high throughout the year. We hypothesize that the increased heterotrophic carbon was the consequence of increased allochthonous carbon being shunted through the microbial foodweb; the energy generated was not likely transferred to zooplankton and passed on to higher trophic levels. More research into the dynamics of allochthonous and autochthonous carbon in eutrophic environments is called for.</p

Ecosystem health of Lake Vänern: Past, present and future research

<div><p>The large lakes of Sweden (Vänern, Vättern, Mälaren and Hjälmaren) have been monitored for more than four decades for water quality conditions to assess the impact of eutrophication from anthropogenic activities. Lake Vänern is basically an oligotrophic lake that showed signs of eutrophication, notably the emergence of algal blooms in the coastal areas (1967–1968). The lake was also contaminated, due to the discharge of pulp and paper effluents including metals such as mercury. However, ecosystem-based information is lacking for Lake Vänern. Consequently a symposium was organized in 2012 by the University of Gothenburg, Mötesplats Vänersborg and the Aquatic Ecosystem Health and Management Society to: assess the current status of the health of Lake Vänern's ecosystem, identify knowledge gaps and develop a road map for the future. In this regard, Lake Vänern was compared with the North American Great Lakes to learn from their extensive, long-term data sets. A special issue devoted to the “State of Lake Vänern Ecosystem” symposium was published in <i>Aquatic Ecosystem Health and Management</i> (<i>AEHM</i>, Vol. 17, no. 4) including keynotes and contributed papers. The conclusions shown in the appendix (available in the online supplementary information) summarize the authors' contributions. Most of the articles covered Lake Vänern, but some were directed towards monitoring and management of Great Lakes in general, and others addressed co-operation under the auspices of international agreements and directives. Based on the background information provided by the State of Lake Vänern Ecosystem symposium and its publication in the special issue, the conveners decided that a synthesis of the symposium with recommendations for the future would be useful in boosting ecosystem research in Lake Vänern.</p></div

The phytoplankton community of Lake Ontario in 2008: Structure, biodiversity and long term changes

<div><p>The phytoplankton community of Lake Ontario was assessed during April, July and September 2008 as part of the Cooperative Science and Monitoring Initiative (CSMI) framework. Results were also compared with historic surveys that began in 1970. A total of 320 unique species were identified during 2008, the vast majority being considered ‘rare’ or ‘less common’. The biomass was found to be, on average, 1.6 g m⁻³ in spring, 3.0 g m⁻³ in early summer and 2.4 g m⁻³ in late summer with rare and less common species accounting for 60–80% of the total. Analysis of the size structure of the phytoplankton community combined with size fractionated primary productivity experiments revealed that one picoplankton (<2 μm) species, <i>Chroococcus dispersus</i> var. <i>minor</i>, accounted for up to half of the observed primary productivity, despite contributing 1% or less to total biomass. Our results also showed that the lake was mesotrophic during the summer of 2008 (July and September) and that trophic state has fluctuated between hyper-eutrophic and ultra-oligotrophic since monitoring began in 1970. These findings demonstrate that the Lake Ontario ecosystem is continually changing and more frequent sampling is needed. A high level of taxonomic expertise is required for even the most basic assessments of the phytoplankton community structure and improved taxonomic training and implementation of standardized techniques are necessary.</p></div

Phytoplankton ecology of a culturally eutrophic embayment: Hamilton Harbour, Lake Ontario

<p>Hamilton Harbour is a chronically eutrophic embayment located at the western end of Lake Ontario that has experienced many decades of agricultural, industrial, and urban contamination. It has been identified as an Area of Concern under the terms of the Great Lakes Water Quality Agreement between Canada and the United States. This study examines the ecology of the phytoplankton communities at one centrally located station during the ice-free period (May–October) of three non-consecutive years: 2002, 2004 and 2006. This was the first comprehensive study to be conducted since the 1970s. It was found that the phytoplankton communities are diverse and fluctuate throughout the year, along with changing nutrient, physical and environmental conditions. No consistent patterns of seasonal succession were observed throughout the study. Phytoflagellates including Cryptophyceae and Dinophyceae had a tendency to outnumber and out-compete other phytoplankton since they are mobile and able to seek out optimal habitats within the water column. For a highly eutrophic water body, algal biomass (annual mean ≈ 2.0 g m⁻³) was lower than expected and more consistent with mesotrophic conditions–an observation first made by researchers in the 1970s and attributed to the highly variable physical environment. While our study supports these earlier results, we also conclude that zooplankton grazing likely has a significant role in limiting the size of the algal standing crop. Several algal bloom events were captured during our study. In addition to the somewhat predictable blooms of Diatomeae in the spring and Cyanophyta in the summer, we also observed blooms of Cryptophyceae and Dinophyceae. In one case we observed a bloom with no dominant taxon–it contained a diverse mixture of Cryptophyceae, Euglenophyta and Dinophyceae–challenging the commonly held notion that algal blooms are essentially monocultures. Our results show that such a variable and stressed ecosystem requires frequent sampling to capture the rapid changes that occur.</p

Phytoplankton ecology in the Bay of Quinte, Lake Ontario: Spatial distribution, dynamics and heterogeneity

<p>The Bay of Quinte, a large riverine embayment located on the northeastern shores of Lake Ontario, has a long history of cultural eutrophication. While the Bay has been the subject of an extensive research and monitoring program that began in 1972, phytoplankton assessments have been limited to 2–3 index stations with few exceptions. Our study consisted of three separate surveys conducted during the summer of 2010 (June, August, September) at 12 sites spread evenly throughout the Bay. Among the major findings were that conditions in the Bay ranged from oligo- to mesotrophic in June, but were primarily eutrophic in August and September with algal blooms observed at 50–75% of the sites; the spatial extent limited only by incursions of oligotrophic water from Lake Ontario. Furthermore, primary productivity in the Bay (e.g. 43.3–109.6 mg C m⁻³ h⁻¹ in September) was among the highest reported in the Great Lakes, indicative of a phytoplankton community very well adapted to its environment. We also found that the Bay of Quinte supported a diverse algal flora containing 140 unique species in June, 209 in August and 169 in September which we attribute to the variable physical environment. Of the 35 phytoplankton samples assessed, Diatomeae were the most prevalent taxa in 16 of those assemblages followed by Cyanophyta (including many toxigenic species) in 12. The relative importance of diatoms are often overlooked in studies of eutrophication yet two species in particular, <i>Aulacoseira granulata</i> and <i>A. ambigua</i>, were major contributors to both the algal standing crop and the elevated rates of primary production. We recommend that future research be directed at understanding the ecology, physiology and dynamics of these filamentous diatoms as well as their associations with filamentous and colonial cyanobacteria.</p