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[1] Differential heating of surface waters of lakes caused by shading from vegetation can induce convection, which could be significant for the ecosystem because the chemistry and biology can differ in the reed belt zone compared to the open lake. This process has been given little attention in the literature. In the present study surface currents just outside a reed belt as well as radiation and water temperature profiles within and outside the vegetated belt were measured in a shallow lake in southern Sweden to determine the lateral flux between the two zones. The measured surface current directed toward the vegetation was about 1 cm/s. Net radiation at the water surface was 85% lower within the vegetation than in the open lake. The water surface temperature during sunny days was on average 0.5°C warmer outside the reed belt, and at maximum 1°C warmer. The lateral heat flux from the open water into the water within the reeds was estimated to $200 W/m 2 during midday on sunny days, which corresponded to a calculated maximum current of 1.5 cm/s. This current between the open water and the reed vegetation is presumably the main water exchange process between the two zones during sunny summer days with low wind speeds.Citation: Lövstedt, C. B., and L. Bengtsson (2008), Density-driven current between reed belts and open water in a shallow lake, Water Resour. Res., 44, W10413,

Wave damping in vegetation in shallow lakes reduces resuspension and thereby improves the light climate and decreases nutrient recycling. In this study, wave transformation in reed (Phragmites australis) was measured in a shallow lake. Theoretical models of wave height decay, based on linear wave theory, and transformation of the probability density function, using a wave-by-wave approach, were developed and compared to the collected data. Field data showed an average decrease in wave height of 4-5% m -1 within the first 5-14 m of the vegetation. Incident root-mean-square wave height varied between 1 and 8 cm, which is typical for the studied lake. A species-specific drag coefficient, C D , was found to be about 9 (most probable range: 3-25), and the model was relatively insensitive to moderate variations in this parameter. The coefficient showed little correlation with aReynolds number or a Keulegan-Carpenter number. The probability density function for the wave height did not change significantly, but for longer distances into the vegetation and higher incident waves it tended to be less similar to a Rayleigh distribution and more similar to the theoretically developed transformed distribution, where the higher waves are more damped than the smaller. Relationships developed in this study can be employed for management purposes to reduce resuspension and erosion in shallow lakes.

Sediment resuspension can significantly affect the light climate and internal nutrient loading in shallow lakes. To predict wind-induced resuspension, a critical bottom shear stress or critical depth for the whole lake is typically used. It is suggested here that the availability of resuspendable material must also be considered and that this availability depends on local wind characteristics. The objective of this study was to show a connection between patterns of resuspension and accumulation of sediments and the prevailing wind directions. The near-shore sediments in the shallow Lake Krankesjçn (surface area = 3 km 2 ) in southern Sweden were characterized by a 5-graded resuspension potential scale and organic content. The spatial variability in sediment characteristics was compared to local wind statistics. This comparison showed that bottoms with low resuspension potential (sandy with low organic content) were located where waves from prevailing wind direction were acting, and bottoms with high resuspension potential (soft sediments with high organic content) were located to the lee-side of the prevailing wind directions. Intensive continuous turbidity measurements showed that winds above 10 m/s in directions other than the prevailing ones brought much material in suspension, while winds in the prevailing direction did not cause any increase in turbidity. The prevailing winds erode the bottom on one side of the lake, depositing resuspended material predominantly on the opposite side, where it can be resuspended by winds from nonprevailing directions. Information about the local wind pattern can improve modeling and understanding of resuspension and redistribution of sediments in shallow lakes.

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