wetlands and biodiversity

Integrated Bufferzones  

Photos:  Integrated Buffer Zone before and during flooding.
Drainage of agricultural land is often a prerequisite for food production in countries with humid climate. Drainage pipes however, creates a direct and rapid contact between arable fields and recipient and act as underground highways for water and nutrients. Current drainage losses account for up to 60% of the total nitrogen losses and about 30% of the phosphorus losses in regions with intensive agriculture.  

Leakage of nutrients from agricultural land through drainage is one of the major problems in the Baltic Sea drainage basin, with major negative impacts on the marine environment. To ensure the good ecological status of the Baltic Sea and in our water courses we need new innovative methods.

By use of the Integrated Riparian takes a holistic approach to the land-water-nutrient-cycle in our production system and breaks the one-way transport of nutrients from the catchment to the sea. Instead we get a more closed system with retention, immobilization and re-cycling of nutrients and the attenuation of flood peaks.

The design allows farmers to benefit directly from ecosystem services such as nutrient re-circulation, controlled drainage and biomass production.

The concept is area-efficient and involves only minor intrusion on productive agricultural land. Integrated protection zones are thus multifunctional and lead to "win-win" situations for farmers and agricultural production systems while reducing the nutrient transport to the Baltic Sea and increases the chances of achieving several of the Swedish environmental objectives and the EU's Water Directive.
Technical principle for an Integrated Buffer Zone (IBZ)

Demonstration site at Little Böslid of an Integrated Buffer Zone with photos taken at low water in 2012 and 2014. Already the third year after startup a rich vegetation with mostly alder was established spontaneously. The fields are to the left with the drain pipes entering into the closed collection ditch. The stream is outside the picture to the right.

Trees affect the infiltration characteristics of soils in several ways: Leaves dragged down by worms causing large holes. After a while, when more and more leaves have accumulated on the surface the infiltration bank is protected even against hard rain effects, which out on the naked field can quickly close all open soil pores.

The wind creates mechanical vibrations and also moves the trunk so that openings in the soil around the trunk develop. Along the finer roots, a thin water-film forms that can distribute the water further. During summer a lot of water is absorbed by vegetation and evaporates into the air.

Function of the IBZ
The integrated buffer zones are placed like the traditional protection zones along watercourses. The width is 10 m, but may vary, and about 70-100 m long, depending on the topography. The integrated buffer zones consist of two segments, a water-filled collecting ditch and a infiltration bank.

Parallel to the watercourse a ditch is excavated that cut the drain pipes that normally discharges into the watercourse. On the other half of the integrated protection zone, closest the river, the ground level is lowered by removing about 10-15 cm of topsoil and spread out on the field, so that an infiltration bank formed. The excavation is done so that the infiltration bank is completely flat and horizontal. The closed collection ditch is about 4 m wide at the crest and the infiltration bank at least 4 meters wide. However, it can be designed considerably wider and have irregular shape, subject to availability of suitable land.

A control well (of the model “Halland level well") is placed in the ditch, with an outlet to the water course at a level about 10 cm above the level of the infiltration bank. The outlet level can if necessary be lowered all the way down to the bottom of the ditch. When it rains and the water starts to flow in drain pipes, the water level in the ditch raises up to cover the infiltration bank. This can be an advantage in summer when the water can be saved by the increase of the water table. At even more rain, when the infiltration bank is not able to receive extreme amounts of water, surplus water is evacuated just above the level of infiltration directly into the watercourse.

When it is instead the other way around, and fields should be as dry as possible, for example, when they should be plowed or harvested, the water level can be temporarily very easily and quickly lowered by lowering the water level in the outlet well to a level near the ditch bottom. On the infiltration bank trees are planted (or allowed to established naturally) because this increases the infiltration capacity many times (up to 60 times). After 10-15 years the biomass can be harvested, and the sediments in the trench excavated. Nutrients are not only barred from reaching the watercourse but they are also re-circulated in a smart and sustainable way.

Level control with the "Halland level well"
The insert pipe can be easily lifted out if no seal rings are used.

 wetlands tjänster projekt_swe
© Peter Feuerbach