How would selection against heterozygous individuals over many generations affect the frequencies of homozygous individuals? would the results of such selection depend on the initial frequencies of p and q? could you test this experimentally?

The selection against the heterozygous individuals would influence the frequencies of the homozygous individuals for many generations. If the selection of heterozygous individuals is not done, the frequency of the heterozygous individuals may decline in against the homozygous individuals.  

Yes, the outcomes rely upon the initial frequencies of p and q of Hardy-Weinberg allele frequencies. An inference can be formulated in order to test the experimentation. For example, use Hardy-Weinberg equation for allele frequencies in a population, that is,  

p2 + 2pq + q2 = 1, where p and q are the homozygous individuals, and 2pq is heterozygous. In the mentioned equation, the heterozygous individuals, that is, 2pq decreases and homozygous individuals, that is, p2 and q2 increases.  

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.