Hamish C. Duthie

Epilithic diatoms as indicators of stream total N and total P concentration

Patterns of diatom species distribution in relation to total N (TN), total P (TP), and other environmental variables from riffle sites on 2 streams in southern Ontario, Canada, were determined using canonical correspondence analysis (CCA). Relationships with TN and TP were sufficiently strong to develop weighted-averaging (WA) regression-calibration models for inferring stream water concentrations of these nutrients. The models were accurate within ±2.4 μg/L for TP (apparent r2 = 0.52) and ±2 mg/L for TN (apparent r2 = 0.53). An evaluation of the goodness of fit of these models with and without bootstrapping indicated that they performed better (bootstrapped r2 = 0.44 for TP and bootstrapped r2 = 0.42 for TN) than published TN and TP inference models for which similar assessments were made. Based on Organisation for Economic Cooperation and Development eutrophication ratings, the TP model predicted 76% of the mesotrophic and 57% of the eutrophic samples correctly. The model correctly predicted only 20% and 33%, respectively, of oligotrophic and hypereutrophic samples. WA inference models were improved when seasonal variation was removed by using mean summer water quality and diatom data (apparent r2 = 0.76 and bootstrapped r2 = 0.61 for TP; apparent r2 = 0.82 and bootstrapped r2 = 0.70 for TN). Overall, we conclude that epilithic diatoms can be related to TN and TP using these methods, and that WA inference models have utility for indicating eutrophication in southern Ontario lowland streams.

Models of aquatic plant productivity: a review of the factors that influence growth

Abstract Models that simulate production of rooted macrophytes and macroalgae in aquatic systems aid in developing hypotheses about the feedback mechanisms that influence plant growth and allow water resource managers to predict how plants will respond to changes in water quality management regimes. Light availability, water temperature, water velocity, and phosphorus, nitrogen and dissolved inorganic carbon concentrations are the environmental factors most often modelled to influence plant photosynthesis, respiration, washout and decay. The algorithms used to describe these relationships are reviewed, with emphasis placed on aquatic plants in freshwater ecosystems. The factors influencing photosynthesis in aquatic plants have been well-described with mechanistic or theoretical equations. However, research is needed to better describe mathematically the mechanisms involved in plant respiration, washout and decay. Due to the complexity of the interaction of environmental factors influencing plant growth, empirical relationships are unavoidable in productivity models and they can provide useful insight into ecosystem dynamics. However, the robustness of macrophyte simulation models is largely dependent on the rigour with which they are calibrated and verified against natural data representing a broad range of environmental conditions.

Stream epilithic, epipelic and epiphytic diatoms: habitat fidelity and use in biomonitoring

We compared the use of epilithic, epiphytic, and epipelic diatom communities in stream biomonitoring by investigating species composition and relationships with measured water quality variables in two tributaries of the Grand River, Ontario, Canada. Although ordination showed some separation of the epilithon from other habitats, clear habitat preferences and seasonality were not identified. Canonical correspondence analysis showed that measured water quality variables explained the major gradients in the diatom data for all three habitats. The diatoms from each habitat were strongly related to alkalinity, suspended solids, biological oxygen demand and conductivity, and in addition, epipelic and epiphytic diatoms showed significant relationships with total phosphorus. It was concluded that although some species were more abundant in one habitat than the others, the community structure of the epilithic, epiphytic and epipelic habitats from these streams was not consistently different. The results indicate no apparent benefit to sampling discrete habitats for water quality monitoring using diatoms, however, the best relationship are obtained using the sum of the diatom data from all three habitats.

PERIPHYTON COLONIZATION OF ROCK SURFACES IN A BOREAL FOREST STREAM STUDIED BY SCANNING ELECTRON MICROSCOPY AND TRACK AUTORADIOGRAPHY1

Periphyton colonization of natural rock surfaces and granite tiles was followed experimentally in the Matamek River, an acidic (pH 5.5) sixth order boreal stream in northeast Quebec, Canada. Accumulation of chlorophyll a and freshweight algal biomass was logarithmic over a 25 day colonization period. The major colonizers were Tabellaria flocculosa (Roth) Kütz., T. fenestrata (Lyngb.) Kütz., Mougeotia sp., and Eunotia pectinalis (Kütz) Rabh., and its varieties. The microcolonization sequence on granite tiles, followed over 27 days with scanning electron microscopy, showed an initial accumulation of algal cells on the upstream and downstream margins and in depressions, followed by a gradual filling‐in of the flat surfaces. It is hypothesized that the observed slow rate of colonization was due to the high surface tension of the granite substratum and the absence of preconditioning by an organic film. It is further hypothesized that the increase in cellular carbon fixation rates of T. flocculosa measured over a 23 day period using nuclear track autoradiography parallels the development of an algal‐detrital microcosm on the granite tile, and is evidence for the establishment of localized tight nutrient spiralling. It is suggested that the periphyton community may be regarded as a nutrient recycling system at a microenvironmental level which may be especially important in oligotrophic systems.

Regression and Weighted Averaging Models Relating Surficial Sedimentary Diatom Assemblages to Water Depth in Lake Ontario

Diatom assemblages in surface sediment samples in depth profiles from Lake Ontario and from East Lake, a shoreline lake, were analyzed for the purpose of describing the relationship between species distribution and water depth. At both sites species composition varied markedly with sample depth. In East Lake a multiple regression of four habitat groups: benthic, epiphytic, tychoplanktonic, and euplanktonic, against water depth (30 cm–8 m) produced a relationship with a standard error (SE) of 1.5 m. An analysis of the ratio of euplanktonic diatoms to periphytic diatoms over a transect from 3 m to 150 m in Lake Ontario produced a multiple regression with an SE of 11.8 m. In another approach, water depth optima for 91 diatom taxa were developed using a weighted averaging (WA) technique. A good correlation (r2 > 0.9) was found between measured and inferred water depth over the range 3 m to 30 m using a unimodal WA regression model. The transfer functions offer the possibility of inferring Holocene water level changes in Lake Ontario from fossil diatom assemblages in sediment cores.

Nitrogen and Phosphorus Regeneration by Cichlids in the Littoral Zone of Lake Malawi, Africa

Interaction between cichlid fishes of the nearshore rocky littoral zone of Lake Malawi with the epilithic periphyton community was addressed by measuring the importance of the fish community in recycling nitrogen and phosphorus through excretion, defecation, and mortality. A series of in situ fish incubations in 13-L Plexiglas chambers at two islands in Lake Malawi provided evidence that excretion and defecation by rock dwelling cichlids supplies 46% to 48% of both nitrogen and phosphorus demands, calculated using Redfield ratios, to support previously measured rates of periphyton photosynthesis. Fish mortality was estimated to more than adequately supply the balance. Epilithic cyanobacteria are an additional source of fixed N. The role of benthic macroinvertebrates in recycling P and N has not been investigated but may be relatively unimportant based on the nutrient balance reported here. The results support the hypothesis that fish may be important in structuring the epilithic periphyton community composition by imposing a low N to P ratio on the benthic algae, favoring dominance by nitrogenfixing cyanobacteria.

Post-glacial development of a kettle-hole peatland in southern Ontario

Abstract:A kettle-hole peatland in southern Ontario was examined in a two core, multi-component paleoecological study to determine the relative importance of external and internal factors in its lo...

Nutrient cycling by biofilms in running waters of differing nutrient status

The autotrophic and heterotrophic nature of attached algal and bacterial populations in streams was investigated in July and August 1986. Glass slides were colonized in two rivers in Algonquin Park, Ontario, that differed in their concentration of bioavailable phosphorus (P). The importance of three abundant algal species was demonstrated by considering their activities on a cellular level using nuclear track autoradiography (NTA). Community biomass accrual, carbon fixation, and phosphate uptake were monitored at bi-weekly intervals and were generally reflective of that of the dominant algal species in each river. It has been proposed that, in running waters, nutrients do not cycle in place but are continually translocated downstream before being re-used by attached organisms. This mode of recycling was demonstrated by monitoring biotic incorporation, release, and subsequent downstream re-incorporation of radiolabelled P and carbon (C) metabolites at the community and cellular levels. The river with less bioavailable P re-assimilated the P metabolites more quickly, but C re-assimilation was similar in the two rivers. This may account for observations that biomass development in running waters may exceed that predicted from empirical P-biomass relationships. Data presented also provide evidence that the species succession, and consequently the tiered development of a biofilm, was the result of the differing abilities of species to sequester and recycle organic and inorganic nutrients from overlying waters.

Morphology and ultrastructure of teratological forms of the diatoms Stephanodiscus niagarae and S. parvus (Bacillariophyceae) from Hamilton Harbour (Lake Ontario, Canada)

Teratological forms of Stephanodiscus niagarae Ehrenb. and S. parvus Stoermer & Håkansson were observed during a study of diatoms preserved in a radiometrically dated core from Hamilton Harbour (Lake Ontario, Canada). Morphological features and ultrastructures of both species were studied under the light and scanning electron microscope. The valve structure of abnormal forms of S. niagarae appears to be weakly silicified, especially in the central area. The shape of satellite pores are very irregular in comparison with the round shape of the normal specimen. The central fultoportulae are characterized as small tubes extending out of the external valve. Two types of abnormal frustules are present in the population of S. parvus studied. In one type valves are “underdeveloped” and only the siliceous layer and ribs are present, and in the other type the valves are strongly silicified and the areolae are almost completely occluded.The teratological forms of both species appeared in the core sediments after 1911, and both became the dominant components of diatom assemblages after 1970. Their occurrence and increased abundance coincides with records of heavy metal pollution in the harbour.

Physiological modifications related to density increase in periphytic assemblages

Periphytic communities in running waters were examined as they developed on granite rocks, concrete balls and glass slides. At equivalent cell densities, no differences in pigment concentrations, species diversity or production levels were found among the different substrata examined. Development of the assemblage appeared to result from the elongation of short algal filaments which had initially settled on the surface. As these communities matured, a distinct canopy and understory developed. Cellular metabolisms were comparable among the communities. In the understory of the communities, even though the cellular content of chl a and b did not differ, chl c and carotenoid pigment concentrations were higher than those in the over‐story.