Environmental DNA
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A Environmental DNA surveys look for genetic material that organisms release into water. The material is often scarce and unevenly distributed, so collection and filtration procedures must limit both loss and contamination. B The field line starts with a measured volume of water and ends with captured material protected for transport. Gloves, clean tubing and negative controls help reveal DNA introduced by the equipment or the operators. C Water is first collected in a sample bottle. A peristaltic pump then moves it through flexible tubing without the water contacting the pump mechanism. The stream enters a filter capsule whose membrane retains particles and DNA-bearing material. D After the measured volume has passed through, a preservation buffer is added to limit degradation. The sealed capsule is placed in a transport bag and kept under the temperature conditions specified by the survey protocol. E In the laboratory, DNA is extracted from the filter and tested with target-specific or broader genetic assays. A positive detection must be interpreted alongside controls, water movement and the possibility that DNA travelled from another location. F The drawing shows one enclosed filtration method. Open membrane holders and precipitation methods are alternatives, and no method guarantees that failure to detect DNA proves a species was absent.