'Duemmer' is a shallow lake in the south-west of Lower Saxony; through the lake flows the river 'Hunte'. The catchment area spans 426 km2. With a surface of 12.4 km2 and an average depth of 1.1 m there is a water volume of approx. 14 million m3. Large parts of the lakeside are a nature reserve and the lake is a popular local recreation area. The lake suffers from strong nutrient contamination by intensive agriculture. Especially in the summer months this causes heavy algae growth and sometimes considerable oxygen deficiency.
In line with a remediation project, a beck called 'Born', which is an important inflow into the 'Duemmer' was redirected in order to reduce the nutrient input into the lake. This measure should be accompanied by adequate monitoring
In addition to the existing measuring network, a compact quality monitoring station, operated by the NLWKN / Sulingen should be set up at the 'Duemmer' outflow Lohne. Parameters to be measured: temperature, conductivity, pH/ORP, dissolved oxygen, turbidity and chlorophyll- a.
Current measured data should be recalled via the GSM radio network and the station shall be addressable 24 h / 365 days. For future applications the station should already be designed for active data sending via GPRS.
Conventional quality monitoring stations cause very high current costs, especially due to maintenance and power
consumption for complicated pumping systems. The NLWKN wants the new station to be a test installation to verify the feasibility of complementary quality monitoring with multiparameter pobes which are installed directly in
the water body.
Since 12/2008 this measuring site is equipped with a compact quality monitoring station with a Hydrolab DS5X multiparameter probe and OTT DuoSens stationmanager , connected with a GSM modem with GPRS option.
The design of this stations allows taking measurements directly in the water body. The probe is installed in a well pipe with slots at the bottom. The connected OTT DuoSens stationmanager controls measurements, data storage and communication. Thanks to open data protocols and formats the integration into existing IT structures is easy. A compact RAL painted control cabinet on a pedestal offers enough space for all components.
The Hydrolab DS5X multiparameter probe is equipped with the following high-class sensors:
- Maintenance-free optical oxygene sensor (LDO)
- Selfcleaning optical turbidity sensor
- Longterm-stable conductivity sensor with 4 graphite electrodes („Bull's Eye“)
- pH-/ORP sensor with robust glass electrode and refillable reference standard
- Fluorometric chlorophyll-a-sensor
- Wiper for all sensors for long operating life
- Cost-saving solution without expensive pumping technology
- Low priced installation thanks to deliberate design with minimum construction and installation work
- Low power consumption (solar power is possible)
- Flexible data communication concept for data recall and with active data transmission (GPRS, SMS)
This system of an in-situ quality monitoring station with a multi parameter probe like it is being used at the 'Duemmer' lake has been continuoulsy delivering reliable data since 2008 at very low operating costs. Employment of such a system can be recommended e.g. at locations where additional QM stations are required on short notice or where existing stations cannot be continued for economic reasons. Even temporary employment makes sense since the installation work is minimal.