Could somebody evaluate my writing for the integrated writing task?

[Zygis]

Hi everyone, I'm taking the TOEFL test on February 11th. Could somebody evaluate my writing? I think I've covered the most essential point but I'm concerned about my grammar.
1)
In this set of materials, the reading passage states some positive facts about giving rewards to employees, and the listening passage casts doubt on the ideas in the reading passage explaining why rewards in enterprise are not beneficial. The reading passage states that rewards increase productivity of employees. Rewards are believed to amend employee attitudes, motivation, and productivity. Also, the reading passage discusses that rewards must have a high perceived value to the employee to reach the best results. Therefore, the reward system has to be correctly structured. The listening passage refutes the advantages of giving rewards to employees. It states that people typically do not like being rewarded, in fact, they merely want to be paid for their work. The listening passage discusses that rewards do not increase productivity as it is mentioned in the reading passage. Instead, rewards tend to diminish productivity. The listening passage also states that productivity is seen as a punishment by employees because people understand being manipulated. Furthermore, it is said in the listening passage that rewards can damage the relationships between an employee and a supervisor since the employee may be reluctant to tell the information to the supervisor which can negatively affect him. Therefore, giving rewards is not beneficial for companies, as it was stated in the reading passage.

2)

In this set of materials, the reading passage provides some advantages of tidal power, and the listening passage casts doubt on the tidal power effectiveness by giving some drawbacks of this exploitation of energy.
The reading passage states that structures can be built to exploit the potential energy formed by tides. When water rises, it flows into the area behind barrage and when the water level drops, the gates are opened and the flowing water generates energy. The reading passage also states that this kind of energy is renewable, non-polluting and can be a useful supplement to other sources of energy.
The listening passage, however, states a few disadvantages of the tidal power. Though the tidal power is non-polluting, it can still negatively affect the environment because this kind of exploiting energy changes the quality of water, and, thus, can harm the fish and birds' populations. To illustrate, barrages may hamper fish migration. Moreover, it is mentioned in the listening passage that fishers would no longer be able to navigate while fishing if the tidal power structure was built. The lecturer suggests that though there are some advantages to exploiting tidal power, the drawbacks of this exploitation ought to be well considered also.

Thanks in advance

TOEFL listening discussions: A conversation between two university instructors

[Luschen]

Hi, I think your writing sounded wonderful. Only a few "nit-picky" errors I could find. I would question your word - "barrage".

[Luschen]

Hi, I think your writing sounded wonderful. Only a few "nit-picky" errors I could find. I can't imagine it not getting the highest score.

[Zygis]

Thank you very much! :)
1)About the word "barrage". It was stated in the reading passage: "this allows water to flow into the area behind the barrage", so I thought this word was OK :\
2) Could you please explain the difference between the words amend and improve? To my knowledge, these two words (and ameliorate, too) are interchangeable when the meaning is - "to make something better".
Thanks again.

[Luschen]