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[1] In this study we prove the feasibility of the advanced very high resolution radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer sea surface temperature algorithms to derive operational lake surface water temperature (LSWT). A validation study covering 2 years was done using data from the AVHRR on NOAA 12, 15, 16, and 17, the MODIS on TERRA, and AQUA and with different method-ingested in situ data from different sized lakes. Best results were found for NOAA 16 nighttime data at Lake Geneva (bias of 0.18 K and standard deviation of 0.73 K) and TERRA nighttime data at Lake Constance (satellite-buoy bias of −0.08 K and standard deviation of 0.92 K). For all sensor families an overall scatter ranging from 0.9 to 1.6 K was found. Bias of MODIS is larger, −1.73 to 1.9 K, than the one of the AVHRR (−0.28 to 1.5 K). The current orbital configuration of the platforms used revealed the diurnal evolution of the lake surface temperature amplitude from space. The damped mixing found for a typical calm and clear-sky regime is different from open ocean conditions. As the main error source, we found undetected cloudy pixel. Furthermore, the physical difference between skin and bulk temperature, especially its relation to the diurnal thermocline, solar insolation, and wind stress contributes to the bias and scatter within the match-up data set. The data sets have been validated to allow further application for LSWT climatology and assimilation into numerical weather prediction models.

Bio-optical measurements were carried out on eutrophic Lake Zug and oligotrophic Lake Lucerne, to provide data and models for the in situ calibration of multispectral imagery collected in 1991, during an AVIRIS flight over Central Switzerland. The results indicate that Secchi depth, chlorophyll and total suspended solid concentrations, vertical extinction coefficient, absorption coefficient and irradiance reflectance in the PAR region can be used to discriminate between the two lakes. Dissolved organics concentration, scattering and total attenuation coefficients estimates, as well as backscattering probability, are less acceptable, because of instrumental limitations. Relationships between optical and water quality parameters were investigated and found to behave according to accepted theoretical frameworks. Both lakes exhibited vertical and horizontal heterogeneities in chlorophyll and turbidity, and had contrasting mean bio-optical characteristics: although suspended solid concentrations were similar, transparency was lower in Lake Zug, but reflectance was substantially higher in Lake Lucerne. Water colour determined by chromaticity analysis was blue-green in Lake Lucerne and green in Lake Zug. Reflectance spectra simulated through a three-component optochemical model did not completely match those derived from in situ measurements, because of lack of site-specific optical cross-sections for suspended minerals and dissolved organics. The monitoring of water quality in subalpine lakes by remote sensing, both with present and future technology, is discussed and considered as possible, provided that their optical behaviour is known, and preferably expressed by a valid optochemical model.

The current level of knowledge concerning Lake Erie is inadequate for the development of a predictive model of the system. Nevertheless, an outline of the submodels required for the development of a predictive model is presented. Further, as a result of many recent studies, the level of understanding of the Lake Erie system has increased immensely and major gaps in the present knowledge of the lake have been identified; useful areas for future research have been indicated. Many of the recent studies on Lake Erie are included in this special issue. The results of these investigations have been summarized and linked together where possible, to describe the lake and give an overview of the more important processes in Lake Erie.

A one-layer, two-dimensional computer model for the time-dependent, lakewide advective and diffusive transports as well as physical regeneration of total phosphorus in Lake Erie has been developed. It has 60 × 16 square grid cells of 6.67-km mesh size and uses a time step of 12 h. The model has been verified and found to be in reasonably good agreement with the Canada Centre for Inland Waters (CCIW) monitor cruise data for October, November, and December during which period there were high winds with high phosphorus concentrations being observed. Computed, daily averaged currents from a hydrodynamic model developed at CCIW are used for the transport terms and actual data for the lake boundary conditions. The physical regeneration is attributed to wave motions induced by wind. A formula is proposed which expresses the regenerated amount of total phosphorus in terms of wave orbital velocity and sediment mean grain size. A discussion is presented on the choice of the settling rate and the regeneration coefficient which produce satisfactory model results.

A budget for phosphorus retention in Lake Erie during 1970 has been drawn up. Phosphorus associated with sand-sized particles (> 63 μm) was excluded. Retention of apatite phosphorus (AP) and nonapatite phosphorus (NAP) within each of the three basins of the lake (Western, Central, and Eastern) was estimated in each case by two independent methods. The two estimates of retention of total phosphorus within the entire lake agreed to within 9.5% of their mean. The estimates of AP retention within the Western basin also agreed well. However, the input–output balance estimates of AP retention in the Central basin and of NAP retention in the Western and Central basins greatly exceeded the corresponding sedimentation values, while in the Eastern basin this pattern was reversed. The AP discrepancy was attributed to unobserved transport of AP from the Central to the Eastern basin via nearshore currents past Long Point, while the NAP discrepancies were largely attributed to eastward movement of NAP through the lake within about 2 m of the lake bottom. The total amount of phosphorus retained within the lake in 1970 was 41,000 metric tons, or about 92% of input. AP of natural origin and inert nature accounted for approximately 44% of the total phosphorus retained. A reduction in anthropogenic phosphorus input of about 15,000 metric tons/yr, as called for in the Great Lakes Water Quality Agreement, will reduce present annual NAP loading to close to pre-1850 values.

On étudie l'influence des rejets de deux stations d'épuration sur la teneur des sédiments côtiers en phosphore, fer et carbone organique. Ces deux stations sont situées sur le littoral lémanique, l'une à Lausanne (Vidy), l'autre à Morges. La quantité de phosphore des sédiments situés dans la zone de rejet de Vidy excède dix fois la teneur naturelle. Les très fortes valeurs trouvées également pour le fer indiquent qu'une pattie du complexe ferro-phosphaté formé lors de l'épuration est relâchée avec les effluents. Les effets de la station de Morges sont moins marqués et ne sont pas visibles dans la distribution géographique du phosphore total dans les sédiments. En revanche, l'utilisation des rapports [fer extractible]/[phosphore non-apatite] et [carbone organique]/[phosphore organique] montre que les effluents de la station de Morges ont enrichi les sédiments côtiers en phosphore à presque deux fois la teneur naturelle. Ces rapports semblent être de meilleurs indicateurs de l'enrichissement des sédiments que les valeurs du P total.