Herman J. Gons

The impact of climate change on lakes in the Netherlands: a review

Climate change will alter freshwater ecosystems but specific effects will vary among regions and the type of water body. Here, we give an integrative review of the observed and predicted impacts of climate change on shallow lakes in the Netherlands and put these impacts in an international perspective. Most of these lakes are man-made and have preset water levels and poorly developed littoral zones. Relevant climatic factors for these ecosystems are temperature, ice-cover and wind. Secondary factors affected by climate include nutrient loading, residence time and water levels. We reviewed the relevant literature in order to assess the impact of climate change on these lakes. We focussed on six management objectives as bioindicators for the functioning of these ecosystems: target species, nuisance species, invading species, transparency, carrying capacity and biodiversity. We conclude that climate change will likely (i) reduce the numbers of several target species of birds; (ii) favour and stabilize cyanobacterial dominance in phytoplankton communities; (iii) cause more serious incidents of botulism among waterfowl and enhance the spreading of mosquito borne diseases; (iv) benefit invaders originating from the Ponto-Caspian region; (v) stabilize turbid, phytoplankton-dominated systems, thus counteracting restoration measures; (vi) destabilize macrophyte-dominated clear-water lakes; (vii) increase the carrying capacity of primary producers, especially phytoplankton, thus mimicking eutrophication; (viii) affect higher trophic levels as a result of enhanced primary production; (ix) have a negative impact on biodiversity which is linked to the clear water state; (x) affect biodiversity by changing the disturbance regime. Water managers can counteract these developments by reduction of nutrient loading, development of the littoral zone, compartmentalization of lakes and fisheries management.

Optical remote sensing of chlorophyll a in case 2 waters by use of an adaptive two-band algorithm with optimal error properties

Two-band algorithms that use the ratio of reflectances at 672 and 704 nm have already proved successful for chlorophyll a retrieval in a range of coastal and inland waters. An analysis of the effect of reflectance measurement errors on such algorithms is made. It provides important indications of the range of validity of these algorithms and motivates the development of an entirely new type of adaptive two-band algorithm for hyperspectral data, whereby the higher wavelength is chosen for each input spectrum individually. When one selects the wavelength at which reflectance is equal to the reflectance at the red chlorophyll a absorption peak, chlorophyll a retrieval becomes entirely insensitive to spectrally flat reflectance errors, which are typical of imperfect atmospheric correction, and is totally uncoupled from the retrieval or an estimation of backscatter. This new algorithm has been tested for Dutch inland and Belgian coastal waters.

Estimating phytoplankton primary production in Lake IJsselmeer (The Netherlands) using variable fluorescence (PAM-FRRF) and C-uptake techniques

In this paper we compare measured rates of C-fixation obtained using in situ deployment of a fast repetition rate fluorometer (FRRF) applying two different calculation protocols and a waterPAM fluorometer. The measurements were carried out in the large, shallow Lake IJsselmeer (The Netherlands). Turbidity appears to be the most important factor in explaining photosynthetic parameters. Non-photochemical quenching (NPQ) in the antenna was observed, and the degree of NPQ was positively correlated with the irradiance and mixing conditions. However, NPQ did not affect the functional cross-section. Conversion of photosynthetic electron transport rates (ETR) into rates of carbon fixation requires knowledge of two or three parameters (depending on the protocol and instrument used) to calculate C-fixation from ETR: the electron yield (Φe, i.e. the reciprocal of the quantum requirement of PSII), the photosynthetic quotient (PQ) and the number of PSII (nPSII). Using normally assumed values for these three parameters resulted in overestimation of the measured rate of C-fixation but, in all cases, ETR was linearly related to it. The degree of overestimation was rather constant, despite considerable changes in phytoplankton composition. Spectral correction of fluorescence data caused a reduction of 30% or an increase of 44% in the estimated C-fixation, depending how C-fixation was estimated. We describe a method that allows estimation of the Φe/PQ ratio based on a comparison of the quantum efficiencies for C-fixation and PSII and show that, with a single and realistic value for this ratio, primary production could be accurately predicted at different times of the year.

Coupling of phytoplankton and detritus in a shallow, eutrophic lake (Lake Loosdrecht, The Netherlands)

An oscillating steady state is described of phytoplankton, dominated by Prochlorothrix hollandica and Oscillatoria limnetica, and sestonic detritus in shallow, eutrophic Lake Loosdrecht (The Netherlands). A steady-state model for the coupling of the phytoplankton and detritus is discussed in relation to field and experimental data on phytoplankton growth and decomposition. According to model predictions, the phytoplankton to detritus ratio decreases hyperbolically at increasing phytoplankton growth rate and is independent of a lakes trophic state. The seston in L. Loosdrecht contains more detritus than phytoplankton as will apply to many other lakes. The model provides a basis for estimating the loss rate of the detritus, including decomposition, sedimentation and hydraulic loss. In a shallow lake like L. Loosdrecht detritus will continue to influence the water quality for years.

Effects of wind on a shallow lake ecosystem: Resuspension of particles in the Loosdrecht Lakes

AbstractHorizontal variation of seston concentration in the shallow, eutrophic Loosdrecht Lakes (A=9.8 km2;

Subsurface irradiance reflectance spectra of inland waters differing in morphometry and hydrology

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The eutrophic Loosdrecht Lakes: current ecological research and restoration perspectives

=1.9 m) was studied in relation to windspeed and effective fetch. Simple wave theory was applied in order to predict resuspension using wind data from a nearby meteorological station. Most results were consistent with the theory, but a clear limit for the occurrence of resuspension could not be established. Generally, changes in epipelon—the particles at the sediment-water interface — were not directly related to computed frequency of resuspension at the sampling station. The frequency was estimated for 37 grid points over the entire lake. Resuspension was computed to affect high percentages of the lake area in winter. In summer the frequency was much lower, but in June and July 1984 there were days with nearly 50% of the lake area subject to resuspension. The resulting input of particulate organic carbon into the water column during these days was estimated to equal 12–25 times the daytime phytoplankton carbon fixation. Most of the resuspended matter appeared to be redeposited rapidly. The computed frequency of resuspension for the 37 locations of the lake varied between 7 and 48 days in 1984.

Periphyton in Lake Vechten, with emphasis on biomass and production of epiphytic algae

Scenedesmus protuberans Fritsch was grown in light-limited continuous cultures with a light-dark cycle, at temperatures of 20° and 28° C. At 20° irradiances of 12 and 38 W m−2 were used, at 28° 38 W m−2.The relationships between growth rate and light uptake rate were of diphasic linear character. With the lower growth rates the relationships were defined with the parameters μe, i.e. the specific maintenance rate constant, and c, the “true” efficiency of light energy conversion into biomass. The μe-value was dependent on temperature, the c on irradiance.In cultures, incubated in prolonged darkness, decrease rates of biomass were comparable to the derived μe-values.Both diphasic linear relationships between growth rate and light uptake rate and the same order of magnitude of μe-values could be derived from literature data on other green algae.