When i review since the beginning of this year, i noticed that my google referred traffic to my site has been declining consistently through the months. Unfortunately, my top keyword has not declined. all my other keywords take up a small percentage of the total traffic each. So is there anyway to investigate further what is causing my consistent google decline?
Try Google Adwords Keyword Tool: https://adwords.google.com/select/KeywordToolExternal You can get an idea on how many people searching for your main keywords. You can even broken it down to how many people in certain countries searched for the keyword as well.
To investigate the reason of decline in the traffic from Google, you should first check that on what keywords you were attracting traffic and compare the current search rankings position with the old rankings. The decline in traffic from Google could happen only if your website ranking gone down and the search trend in your niche has been changes and people are using some other keywords.