Project “Lake Studies” As of October 19, 2022
Summary
In the years 1993-2005, I carried out the monitoring for the lake on behalf of the bathing administration of the bathing lake Buchtzig near Ettlingen-Oberweier. The data from this enables a correlation to be calculated between the TDP/TP ratio and the stocking with roach, as well as the correlation of the total phosphorus (TP) with the biomass of the cladocerae. Two parallel gradients in the regression TP against cladoceran biomass correspond to the model that Scheffer calculated for zooplankton (Scheffer 2004). With these results, the basics of ecology, the different states in an ecosystem and the change between them are addressed. In a continuation of the project, the quality of working equipment would have to be checked for the purpose of filtering water samples in the laboratory and for zooplankton sampling on the lake. Long-term studies on lakes with and without bathing and with and without fishing are appropriate to determine the threshold values between different ecological states.
Introduction
There are more than a hundred artificial lakes in the Upper Rhine Valley and most of them have fishing leases with fishing clubs. The gravel pits have been stocked with fish ever since the quarrying began. The fish stockings are often repeated regularly, also in lake Buchtzig while I was examining the lake. The results from these long-term investigations over 13 years on behalf of the bath administration at the Buchtzigsee are available on the homepage www.p-fraktionen.de for the purpose of examination and post-processing by third parties. A two-page publication was printed in Fischer und Teichwirt 5/2020 (Keim 2020). In addition, the DGL has included my contribution on the results from 1993-2005 for their annual general meeting in Leipzig in their annual report 2022 (Keim 2022). The evaluation of the documents from the Buchtzig bathing lake showed possibilities for recording different ecological conditions and their changes. This has to be continued for the causal analysis of the lake ecosystem.
A lake is exposed to a variety of influences. Lake management to control the influences from human activities is required. Knowledge of the causal relationships is one of the prerequisites for rational management of the lake in order to bring protection, conservation and human use together.
Fish stocking can change the ecological status of a lake and the effect of such fish stocking has been discussed for some time (Tremel 1995). However, there was often no access to the stocking reports from the angling clubs. So far, zooplankton have been evaluated according to the size-efficiency hypothesis (Brooks & Dodson 1965). In fact, the effect of nutrient supply and fish stocks on zooplankton is very complex and requires further investigation.
Reason
So far, there has been a lack of suitable working methods for such work tasks. A fish inventory is time-consuming. The correlation of stocking with planktivorous fish with a limnological parameter is desired. It needs a feature that can be measured with reasonable effort. Zooplankton deserve special attention because they act as a hinge for the effects of nutrient supply (bottom-up) and animal population (top-down). There are probably good working approaches to record the influences on the zooplankton. So far, these have not been sufficient to differentiate bottom-up and top-down in their effect on zooplankton. The work results in the filtration of water samples with the help of gravity and the pump capture of zooplankton are a beginning and to be continued.
In the Leibniz Society, Prof. Arlinghaus works on pike (Arlinghaus et al. 2015). There are publications from North America and France on carp stocking (Crivelli 1983). For many years, Benndorf and his colleagues have studied the effects of predatory fish on the zooplankton at the Bautzen dam (Benndorf 1995). I only know the results from the Buchtzigsee (Keim 2022) for stocking roach. However, the roach is at the top of the list in Central Europe when stocked by fishing clubs.
The results from the Buchtzigsee are so far an isolated case that needs to be checked on other lakes. The field of work is in the Upper Rhine Valley with its many artificial lakes.
Working methodology and equipment question
Tools and working methods for the practice of water management are in demand. That means taking care of the basics first.
What are the advantages and disadvantages of the different devices? Is a device suitable for the purpose and how can I improve it. I may obtain additional material in order to achieve the desired quality of work.
The sampling is taken from the boat in the morning as a depth profile with meter-by-meter measurements of temperature, oxygen concentration, pH value and conductivity. For this purpose, the water transparency as Secchi depth is also measured. Water samples are taken as mixed samples from the epi- and hypolimnion and filtered on the same day. The filtrate and fogged filters are oxidized with potassium peroxodisulfate and the phosphorus is measured the next day. The acid binding capacity is also measured from these water samples.
For water samples from a mountain stream I can use vacum filtration, the solid particles consist of detritus. Water samples from a river, lake or the sea contain living algae cells. Here I have to avoid pressure differences and the filter membrane drying out, otherwise living cells would be damaged (Goldman & Dennett 1985; Kiene & Slezak 2006). So I use gravity filtration in a gentle way: the maximum filling height is one meter, so the filtrate drips and the filter membrane stays wet.
For the zooplankton, the question arises as to how I take the samples and where I filter: when a net is drawn, the mesh fabric is an obstacle, the net meshes clog (Kofoid 1897 a,b) and there are different flow velocities in the area of the net opening (Brandner et al. 1993). For low-density organisms such as pelagic fish eggs and fish larvae in the sea, I can pull a 300 µ mesh net through the open sea. A cylindrical mains part behind the net opening reduces different flow velocities in the net opening. The drag caused by the netting can be compensated for by increasing the number of meshes. The network is constructed longer for this (Smith et al. 1968). The efficiency of the net pull is tested with a flow meter inside and outside the net opening. If the difference between the two measurements is less than 85%, the sample is discarded (Sameoto et al 1983). For the zooplankton in lakes I have to use a netting with a mesh of 100 µ and smaller. The resistance of the netting then becomes too high. So I use a pump and filter the water on the boat. A hose on a reel would cause a lot of friction and thus require very different pump performance (Powlik et al. 1991). The hose is therefore replaced by a pipe system, the individual pipes of which are each one meter long. The filtered water volume is thus easy to record and useful for calculating the density of zooplankton organisms.
I see that important steps have been taken in marine biology in the choice and design of tools. On the other hand, the ecological processes in the sea are extremely complex. Small lakes offer conditions for which some influencing variables are absent. There are no tides and purely pelagic fish species such as the coregones only exist in lakes of less than 80 ha. A small lake therefore offers the opportunity to work on basic questions of ecology, e.g. the change between states with and without planktivorous fish.
Detailed investigations with phosphorus measurements are intended to provide information about disturbances in the relationship between TP and Cladoceren and biomass, possibly caused by the choice of tools or short-term nutrient mobilization from the bank area. Also the relationship of the total phosphorus (TP) with the TDP/TP ratio has to be checked, which influences are disturbing or whether it is possible to establish a correlation at a significant level.
Cooperation with existing research programs on fish stocks is desired. Cooperation with a fishing club is essential. I would like a reliable partner for the lake project, which I am most likely to find in a large club like the Anglerverein Karlsruhe e. V
There are criteria for the quality of the results.
Correlation with other parameters
Coefficient of determination r2: to what percentage is there a dependency
Correlation coefficient, to be calculated from the coefficient of determination and checked against the bounds for significance.
Two parallel slopes correspond to the model predicted by Scheffler for the zooplankton.
Start with practical questions: better tools to avoid unwanted changes in the material during sampling and sample processing. E.g. clogging of the net meshes when the net is pulled, damage to cell walls when the filter membrane dries out. What are the potential disadvantages of pump capture and gravity filtration. To what extent do these affect the work results?
What disturbing influences were there in the Buchtzig bathing lake compared to other lakes?
At lake Buchtzig, a high degree of scattering can be seen in the relationship TP versus the TDP/TP ratio. The regression is therefore not calculated. The question arises as to where, in contrast to the Wilhelmswörthweier, this scattering comes from. Is there an impact from the bathing operation visible here? It partly affects the measurements in July, i.e. at the peak of bathing activity. The July data were also sorted out for the TP regression against the Cladoceran biomass to obtain a significant level calculation.
Investigation program for lake investigations as of October 2022
First year:
1. Device comparison for filtration of water samples via vacuum or gravity
2. Equipment comparison for zooplankton sampling via vertical with the conical net or pump catch
3. Development of a Daphnia breeding including forage algae with Daphnia galeata and D. cucullata and their hybrids
4. Development of a molecular-biological identification of water fleas and fish
5. Start of long-term studies on lakes according to the „Bruchsal model“ with monthly sampling, i.e. pump catch and gravity filtration
Second year:
1. Continuation of the long-term studies for phosphorus, plankton and fish stocks. Where are the stocking fish?
2. What genetic changes do the Daphnia experience before and after fish stocking and without fish stocking?
3. How high and wide does a plankton tower have to be for vertical migration to take place?
4. Tests in the Plankton Tower to determine threshold values in the concentration of bile acids from fish to trigger daily vertical migration
Third year:
1. Continuation of the long-term studies for phosphorus, plankton and fish stocks. Where are the stocked fish?
2. Basic investigations into causal relationships require better detection methods on the lake and in the laboratory. For work that I outsource, I outsource the expertise. Exchange with other laboratories is desirable.
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