Problem 2.

Read the following description of an environmental monitoring study carefully then answer the three questions (a to c) below.

A mine is due to release effluent into two streams in the Wet-Dry tropics (where there are very distinct Wet and Dry seasons, with little to no rain falling during the Dry). A monitoring program will commence two years before the first release and continue for two years afterwards (it may continue after that but this question considers just those four years).

Monitoring will be done on the two impact streams and on two similar streams which will not receive effluent. One element of the program will involve using small nets to catch macroinvertebrates (water bugs) at selected sites on each creek. One site will be upstream, and the other downstream, of the spot where the effluent will be released (see diagram).

Each sampling time, 5 samples will be taken at each of the sites and the number of species of macro-invertebrates will be recorded (this will be done later in the lab).

Sampling is done three times during the Wet season, at monthly intervals, each year.

The sampling schedule is summarised in Table 2 .

Figure 3: Design of study. The diagram below illustrates the physical arrangement of the system and the samples. The two creeks in the centre will receive effluent after two years. The red dotted circles indicate the sampling sites: 5 samples will be taken at each site on each sampling occasion. Effluent flows downstream from the release point below the mine.

Questions:

a) List the factors in the design and give the number of levels in each factor.

b) State, with reasons, which factors are fixed and which are random.

c) State, with reasons, which factors (if any) are nested in other factors.

Table 2: Sampling schedule. This table illustrates the planned sampling program. In this table, “15” means that 15 samples will be collected at that time in that year in that area. The number of samples is 15 because 5 samples are every two months in the Wet Season. (“N/A” means “not applicable”: this column—Sep 15—is included just to indicate when the release of effluent will start.)