The amount of goods transported by water was constant from 1974 to1978, where it showed an exponential growth, rising to almost 60 million tonnesafter which it plateaued for about 20 years before starting to rise graduallyagain.
①where引导的非限拟定语从句是作插入语吗？修饰的是哪个？为何用where而不是when？
②exponential growth是指1974-1978还是1978-1982？
③rising to后面是动词ing作状语修饰句子吗？
你这个文章非常不规范，错误不少, 对图表的讲解也不够准确。假设是四级或雅思写作题，我修改如下：
The amount of goods transported by water remained constant at40 million tonnes from 1974 to 1978. Then it experienced/witnessed an exponentialgrowth, increasing to approximately (比 almost 分高）60 milliontonnes. After that, it plateaued for about twodecades before starting to rise sharplyagain.
原句用where不准确，描述图表时间段时不需要where, 可以用during which.exponential growth是指1978-1982. 原句rising to作状语表示上升的结果。我在改写时添加了一些connectors(连接词），如此使句子之间维持连贯与衔接。最后那句用gradually不准确，改用sharply.
若是段首，习惯上还要加上The graph shows/indicates/demonstrates that... 这里的动词只可以用一般目前时。当然不加这个开头也不算错。
