Papers by Gertrud Nurnberg
Wiley Interdisciplinary Reviews: Water, Aug 30, 2024
Sustainable management of lakes requires us to overcome ecological, economic, and social challeng... more Sustainable management of lakes requires us to overcome ecological, economic, and social challenges. These challenges can be addressed by focusing on achieving ecological improvement within a multifaceted, co-beneficial context. In-lake restoration measures may promote more rapid ecosystem responses than is feasible with catchment measures alone, even if multiple interventions are needed. In particular, we identify restoration methods that support the overarching societal target of a circular economy through the use of nutrients, sediments, or biomass that are removed from a lake, in agriculture, as food, or for biogas production. In this emerging field of sustainable restoration techniques, we show examples, discuss benefits and pitfalls, and flag areas for further research and development. Each lake should be assessed individually to ensure that restoration approaches will effectively address lake-specific problems, do not harm the target lake or downstream ecosystems, are cost-effective, promote delivery of valuable ecosystem services, minimize conflicts in public interests, and eliminate the necessity for repeated interventions. Achieving optimal, sustainable results from lake restoration relies on multidisciplinary research and close interactions between environmental, social, political, and economic sectors.
Science of The Total Environment
Water Quality Research Journal of Canada, May 1, 1997
Research Square (Research Square), Jun 1, 2021
Coloured lakes are often productive. While their increased productivity can be the consequence of... more Coloured lakes are often productive. While their increased productivity can be the consequence of internal recycling of phosphorus (P), the impact of humic substances on these interactions is largely unexplored. Here we elucidated the spatial variations in sediment P release by diffusion in four Finnish lakes with high trophic state. For further insights regarding possible implications of humic substances on sediment P release, we extended our analysis to lakes worldwide using data from the scienti c literature. Variations in sediment P release rates (RR) in four Finnish lakes were largely explained by trophic state and mixing state of the water column. P release by diffusion was positively correlated with the iron-bound P fraction, but negatively with the organic-P fraction in surface sediment. Furthermore, the diffusive ux of P correlated positively with the RR predicted from a published model based on total P concentration (positive effect) and organic matter content (negative effect) in surface sediments. Analysis of the worldwide data con rmed the importance of humic substances in internal P recycling. While dissolved organic carbon (DOC) in water correlated positively with RR in oligotrophic lakes, the correlation was negative in lakes of higher trophic state. The implications for internal P loading and primary production, however, are not so straightforward. In a multiple-stressor world (climate change, eutrophication), response of internal P load in boreal lakes to changes in DOC is particularly unpredictable. This is because the variables relevant to internal P loading, i.e. RR and anoxic factor, may be affected in a reverse direction.
Environmental Science & Technology, Feb 18, 2009
Hypoxia, a growing worldwide problem, has been intermittently present in the modern Baltic Sea si... more Hypoxia, a growing worldwide problem, has been intermittently present in the modern Baltic Sea since its formation ca. 8000 cal. yr BP. However, both the spatial extent and intensity of hypoxia have increased with anthropogenic eutrophication due to nutrient inputs. Physical processes, which control stratification and the renewal of oxygen in bottom waters, are important constraints on the formation and maintenance of hypoxia. Climate controlled inflows of saline water from the North Sea through the Danish Straits is a critical controlling factor governing the spatial extent and duration of hypoxia. Hypoxia regulates the biogeochemical cycles of both phosphorus (P) and nitrogen (N) in the water column and sediments. Significant amounts of P are currently released from sediments, an order of magnitude larger than anthropogenic inputs. The Baltic Sea is unique for coastal marine ecosystems experiencing N losses in hypoxic waters below the halocline. Although benthic communities in the Baltic Sea are naturally constrained by salinity gradients, hypoxia has resulted in habitat loss over vast areas and the elimination of benthic fauna, and has severely disrupted benthic food webs. Nutrient load reductions are needed to reduce the extent, severity, and effects of hypoxia.
Verhandlungen, Sep 1, 2005
Hypoxia and cyanobacteria still occur occasionally in large, mesotrophic Lake Simcoe, and total p... more Hypoxia and cyanobacteria still occur occasionally in large, mesotrophic Lake Simcoe, and total phosphorus (TP) concentration has remained relatively constant despite external nutrient load reduction. This may indicate a potential internal P source. Internal load as redox-dependent P release from bottom sediments is hard to determine in such a relatively shallow and mostly mixed lake. This study represents the first attempt to quantify internal P loading over many years for the three main sections of Lake Simcoe. Internal load was determined (a) as in situ estimate based on TP increases between July and October and (b) as gross estimate from the product of experimentally determined P release rates and hypoxic extent of sediment surfaces in space and time. Hypoxic extent was quantified (1) as the hypoxic factor determined from dissolved oxygen profiles below the level of 3.5 mg/L, and (2) as active sediment area release factor (AA) modeled from summer euphotic TP concentration, which is especially useful in the mixed sections. Annual internal load for the whole lake was determined as a near constant 62.2 metric tonnes/yr (86 mg/m 2 /yr) for 1980-2011 using the gross estimates of the AA approach and 88 t/yr before and 53 t/yr after external load abatement and zebra mussel invasion using in situ estimates. Means of in situ and AA-based estimates for 2000-2011 are in close agreement except for polymictic Cook's Bay. These estimates are 45 to 89% of external load, which suggests that internal loading is an important source of P in Lake Simcoe.
Verhandlungen, Jul 1, 1984
Limnology and Oceanography, Jun 1, 1999
Lake and reservoir management, Jan 13, 2017
Nürnberg GK. 2017. Attempted management of cyanobacteria by Phoslock (lanthanum-modified clay) in... more Nürnberg GK. 2017. Attempted management of cyanobacteria by Phoslock (lanthanum-modified clay) in Canadian lakes: water quality results and predictions. Lake Reserv Manage. 00:1-8. When internal phosphorus (P) loading from the bottom sediments outweighs external P inputs to lakes, lake water quality and cyanobacteria blooms will not respond to external measures alone and therefore require an in-lake restoration treatment. Lake characteristics and governmental regulations do not permit a random choice of such methods. A treatment developed by an Australian research institute (CSIRO) more than 15 years ago has recently been introduced to Canada and is licensed in Ontario. The lake water treatment consists of the application of a phosphate adsorbing and sediment capping agent called Phoslock in North America, a clay (bentonite) that has been systematically amended by the phosphate adsorbing element lanthanum. When applied, Phoslock sinks to the lake bottom where it intercepts the upward flux of internal load from sediment P release. Although the number of monitored Canadian applications is still small, suggestions to optimize restoration effects can be made, including the avoidance of high flushing during application, system isolation, and timing to coincide with high levels of inorganic P in the lake water. Initial results in at least 2 cases (Swan Lake, City of Markham, Greater Toronto Area; and Henderson Lake, Lethbridge, Alberta) were promising despite the unexpected external P input from waterfowl and possibly other external sources. Other applications are planned in a Quebec lake and are being discussed in several other provinces.
Lake and reservoir management, Jan 2, 2016
Canadian Journal of Fisheries and Aquatic Sciences, Aug 1, 1993
Iron mass balances for eight lakes (76 lake-years of data) on the Canadian Precambrian Shield wer... more Iron mass balances for eight lakes (76 lake-years of data) on the Canadian Precambrian Shield were measured including catchment, atmospheric and internal sources of iron. These data were compared to or combined with available data from the literature on iron fluxes in other North American and European Lakes. In most of these lakes, internal iron load was important; it resulted from anoxic sediment release since the lakes' hypolimnia became partly anoxic during summer stratification. Iron retention, based on external iron load only and determined from the ratio of incoming minus outgoing iron mass and incoming mass (R ext), was correlated to internal load and not to morphometry and hydrology of the lake. On the other hand, when internal load was included in the calculated retention, (R tot), retention was correlated with morphometry and hydrology, and not internal load. An average annual settling velocity of iron, computed from the relationship of R tot with the annual water load (q s), ranged from 12 to 26 m yr-1 depending on the data set. A simple mass balance model was used to predict annual average iron concentration. Although model predictions and observed concentrations were significantly correlated, annual average concentrations were underestimated by the model in the Precambrian Shield lakes, but overestimated by atmospherically loaded and acid-stressed lakes from the Sudbury, Ontario region. Inclusion of a term related to organic acid content rendered the mass balance equation more general. Furthermore, the inclusion of dissolved organic acid concentration, colour of the lake water and loss on ignition of the surface sediment proved to be important secondary variables.
Water Research, 1984
Abstract Anoxic water from eight lakes containing various amounts of ferrous iron, hydrogen sulfi... more Abstract Anoxic water from eight lakes containing various amounts of ferrous iron, hydrogen sulfide, calcium and total phosphorus was analysed for soluble reactive phosphorus (SRP). Hydrogen sulfide concentrations higher than 1 mg l −1 and ferrous iron concentration above 0.20 mg l −1 produce interferences in the SRP analysis in many occasions (e.g. 80% underestimation of SRP). Interfering concentrations of these materials are shown to be present in anoxic water from a large number of lakes, groundwater springs and ocean basins. The mechanisms of the interferences are discussed and methods described to prevent these analytical errors. Ferrous iron is not problematic if the sample is kept anoxic before and during filtration. On the other hand vigorous aeration is obligatory if hydrogen sulfide is present. Simple methods to test for both the possible interfering compounds are presented. It is shown for the water from the anoxic hypolimnia of eight lakes that a modified analysis of total (unfiltered) reactive phosphorus (TRP) yields on average only 2% lower phosphorus concentrations than SRP analysis. TRP hence can replace the complicated SRP analysis in anoxic waters.
Water Resources Research, 2004
Lake and reservoir management, Dec 1, 2003
Limnology and Oceanography, Nov 1, 1998
Canadian Journal of Fisheries and Aquatic Sciences, May 1, 1984
The availability of hypolimnetic phosphorus was assessed by a short-term bioassay, based on 32P u... more The availability of hypolimnetic phosphorus was assessed by a short-term bioassay, based on 32P uptake kinetics. In the anoxic hypolimnia of eight lakes and in anoxic model systems (core tubes), at least 80% of soluble reactive phosphorus is biologically available. However, biologically available phosphorus is only a small fraction of soluble reactive phosphorus in iron-rich, previously anoxic waters after aeration and in lake water from the anoxic–oxic interface. This result is supported by published data for oxic waters from epilimnia of lakes, rivers, sewage effluent, and precipitation.
Lake and reservoir management, Dec 10, 2009
Abstract Internal loading as phosphorus (P) released from anoxic sediment surfaces often represen... more Abstract Internal loading as phosphorus (P) released from anoxic sediment surfaces often represents the main summer P load to lakes and reservoirs and can have an immense effect on their water quality. Many difficulties in internal load assessment exist, however, including ignoring internal load altogether, ambiguity about the origin of sediment released P and inexact definitions. Most of these problems are due to the difficulty in distinguishing internal from external P sources, which is particularly challenging in polymictic lakes. To prevent misconceptions and facilitate its evaluation, internal load in stratified and polymictic lakes should be expressed in a similar way to external loads: as annual, gross and areal load of total phosphorus (TP). Possible approaches to internal load quantification are: in situ determination from hypolimnetic P increases, mass balance approaches, and estimates from anoxic active area and P release. Further suggestions to facilitate the study of internal loading include: (a) the differentiation between polymictic and stratified lakes, sections of lakes, and time periods when evaluating indicators and impact of internal load; (b) the separation of internal load (upward flux) from sedimentation (downward flux) of external and internal loads, and (c) the consideration of the downward flux of both external (Lext, mg/m2/yr) and internal (Lint, mg/m2/yr) loads by a retention model (Rsed) when predicting lake TP averages in a mass balance model of the form (qs = annual areal water load in m/yr):
Limnology and Oceanography, 1984
Lakes with anoxic hypolimnia (anoxic lakes) have significantly lower values for phosphorus retent... more Lakes with anoxic hypolimnia (anoxic lakes) have significantly lower values for phosphorus retention than do lakes with aerobic hypolimnia (oxic lakes). This difference may reflect an increased internal phosphorus load from the anoxic hypolimnia. Two models are given to predict internal phosphorus load (L;,,) in such lakes. The first predicts internal load as the difference between the observed phosphorus retention in anoxic lakes and that predicted (Rpred) by a formula that adequately describes phosphorus retention in oxic lakes. The second predicts internal load as the product of an average rate of phosphorus release from anoxic sediments, the surface area of the anoxic sediment, and the period of anoxia. Predictions of the first model compare favorably with 17 observed values of internal load; further data are required to test the second model. These models suggest that mean phosphorus concentration (TP) in anoxic lakes can be predicted in two ways. One can use whole-lake phosphorus budget models which implicilly incorporate internal phosphorus load, because they include a measurement of phosphorus retention. Alternatively, a term to account for the internal load can be added to current models based on external load (L,,,) and predicted retention (I&J, where qs is areal water load: Mass balance models have been widely used to predict the concentration of phosphorus-the major limiting nutrient-in lakes. In these models (e.g. Vollenweider 1969; Schindler and Nighswander 1970; Dillon and Rigler 1974) the mean total phosphorus concentration is calculated as the amount coming in divided by the volume of water coming in and diminished by a retention term which represents the proportion of incoming phosphorus apparently lost to the sediments. Phosphorus retention can be determined from annual nutrient budgets-the mass of phosphorus entering and leaving the lake (Dillon and Rigler 1974)-or predicted from the lakes' morphometric and hydrological characteristics. These models predict that retention lies between 0.0 and 1 .O in all lakes (e.g. Dillon and Kirchner 1975; Larsen and Mercier 1976). Lakes having anoxic bottom water for a significant period show consis-' A contribution to the Limnology Research Centre, McGill University. A grant from the Natural Sciences and Engineering Research Council of Canada to R. H. Peters provided computer money. G.K.N. holds a scholarship from the Social Sciences and Humanities Research Council of Canada for foreign students.
Lake and reservoir management, Dec 1, 1996
Idiosyncrasies, erroneous assumptions and gaps are still hampering lake evaluations, despite seve... more Idiosyncrasies, erroneous assumptions and gaps are still hampering lake evaluations, despite several decades of defining the trophic state of lakes. I reevaluated nutrient and algal biomass limits that group lakes into oligo-, meso-, eu- and hyper eutrophic lakes at transition concentrations of 10, 30 and 100 μg · L average total phosphorus concentration of the summer epilimnion. I investigated the
Transactions of The American Fisheries Society, Sep 1, 1995
The detrimental effect of oxygen depletion on fish is well known. Here a quantitative measure of ... more The detrimental effect of oxygen depletion on fish is well known. Here a quantitative measure of anoxia is compared with the number of fish species in 52 south-central Ontario lakes. The anoxic factor (AF, days per year or per season) estimates the number of days that a sediment area equal to the lake surface area is overlain by anoxic water. It can be expressed separately as summer or winter AF. Stepwise multiple-regression models were constructed with AF and common physical and chemical variables to predict fish species richness. Because some of the parametric regression assumptions were violated, the traditional statistics were evaluated with randomization tests to confirm significance. The best regression models included summer AF or lake surface area, or winter AF and mean depth, for subsets of acidic and circumneutral lakes; these models explained up to 75% of the variation in fish species richness. One of the models can be used to estimate the likelihood of winterkill. Anoxic factor was also correlated with the number of coldwater fish species present. The concept of AF can be used to model the distribution and number of fish species in stratified lakes and should be useful in the management of oxygen-dependent aquatic animals (e.g., tin fish and shrimp) in freshwater and marine habitats.
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Papers by Gertrud Nurnberg